diff --git a/src/Core/Base/Date.php b/src/Core/Base/Date.php
index 43b9bf7489..79a428b205 100644
--- a/src/Core/Base/Date.php
+++ b/src/Core/Base/Date.php
@@ -12,18 +12,15 @@
 
 namespace OnPHP\Core\Base;
 
+use DateTime;
 use OnPHP\Core\OSQL\DialectString;
 use OnPHP\Core\Exception\WrongArgumentException;
 use OnPHP\Core\DB\Dialect;
-use DateTime;
-
-/* $Id$ */
 
 /**
  * Date's container and utilities.
  * 
  * @see DateRange
- * 
  * @ingroup Base
 **/
 class Date implements Stringable, DialectString
@@ -37,40 +34,50 @@ class Date implements Stringable, DialectString
 	const WEEKDAY_SUNDAY	= 0; // because strftime('%w') is 0 on Sunday
 
 	/**
-	 * @var \DateTime
+	 * @var DateTime|null
 	 */
-	protected $dateTime = null;
+	protected ?DateTime $dateTime = null;
 
 	/**
-	 * @return Date
-	**/
-	public static function create($date)
+	 * @return static
+	 * @throws WrongArgumentException
+	 */
+	public static function create($date): Date
 	{
 		return new static($date);
 	}
 
-	public static function today($delimiter = '-')
+	/**
+	 * @param string $delimiter
+	 * @return string
+	 */
+	public static function today($delimiter = '-'): string
 	{
 		return date("Y{$delimiter}m{$delimiter}d");
 	}
 
 	/**
-	 * @return Date
-	**/
-	public static function makeToday()
+	 * @return static
+	 * @throws WrongArgumentException
+	 */
+	public static function makeToday(): Date
 	{
 		return new static(static::today());
 	}
 
 	/**
-	 * @return Date
 	 * @see http://www.faqs.org/rfcs/rfc3339.html
 	 * @see http://www.cl.cam.ac.uk/~mgk25/iso-time.html
-	**/
-	public static function makeFromWeek($weekNumber, $year = null)
+	 * @param $weekNumber
+	 * @param int|null $year
+	 * @return Date
+	 * @throws WrongArgumentException
+	 */
+	public static function makeFromWeek($weekNumber, int $year = null): Date
 	{
-		if (!$year)
+		if (null === $year) {
 			$year = date('Y');
+		}
 
 		Assert::isTrue(
 			($weekNumber > 0)
@@ -99,7 +106,12 @@ public static function makeFromWeek($weekNumber, $year = null)
 		return $date->modify("+{$days} day");
 	}
 
-	public static function dayDifference(Date $left, Date $right)
+	/**
+	 * @param Date $left
+	 * @param Date $right
+	 * @return int
+	 */
+	public static function dayDifference(Date $left, Date $right): int
 	{
 		return
 			gregoriantojd(
@@ -114,15 +126,25 @@ public static function dayDifference(Date $left, Date $right)
 			);
 	}
 
-	public static function compare(Date $left, Date $right)
+	/**
+	 * @param Date $left
+	 * @param Date $right
+	 * @return int
+	 */
+	public static function compare(Date $left, Date $right): int
 	{
-		if ($left->toStamp() == $right->toStamp())
+		if ($left->toStamp() == $right->toStamp()) {
 			return 0;
-		else
+		} else {
 			return ($left->toStamp() > $right->toStamp() ? 1 : -1);
+		}
 	}
 
-	public static function getWeekCountInYear($year)
+	/**
+	 * @param $year
+	 * @return int
+	 */
+	public static function getWeekCountInYear($year): int
 	{
 		$weekCount = date('W', mktime(0, 0, 0, 12, 31, $year));
 
@@ -133,6 +155,10 @@ public static function getWeekCountInYear($year)
 		}
 	}
 
+	/**
+	 * @param $date
+	 * @throws WrongArgumentException
+	 */
 	public function __construct($date)
 	{
 		$this->import($date);
@@ -148,12 +174,19 @@ public function  __sleep()
 		return array('dateTime');
 	}
 
-	public function toStamp()
+	/**
+	 * @return int
+	 */
+	public function toStamp(): int
 	{
 		return $this->getDateTime()->getTimestamp();
 	}
 
-	public function toDate($delimiter = '-')
+	/**
+	 * @param string $delimiter
+	 * @return string
+	 */
+	public function toDate($delimiter = '-'): string
 	{
 		return
 			$this->getYear()
@@ -163,62 +196,81 @@ public function toDate($delimiter = '-')
 			.$this->getDay();
 	}
 
-	public function getYear()
+	/**
+	 * @return string
+	 */
+	public function getYear(): string
 	{
 		return $this->dateTime->format('Y');
 	}
 
-	public function getMonth()
+	/**
+	 * @return string
+	 */
+	public function getMonth(): string
 	{
 		return $this->dateTime->format('m');
 	}
 
-	public function getDay()
+	/**
+	 * @return string
+	 */
+	public function getDay(): string
 	{
 		return $this->dateTime->format('d');
 	}
 
-	public function getWeek()
+	/**
+	 * @return string
+	 */
+	public function getWeek(): string
 	{
 		return date('W', $this->dateTime->getTimestamp());
 	}
 
-	public function getWeekDay()
+	/**
+	 * @return string
+	 */
+	public function getWeekDay(): string
 	{
 		return strftime('%w', $this->dateTime->getTimestamp());
 	}
 
 	/**
-	 * @return Date
-	**/
-	public function spawn($modification = null)
+	 * @param string|null $modification
+	 * @return static
+	 * @throws WrongArgumentException
+	 */
+	public function spawn(string $modification = null): Date
 	{
-
 		$child = new static($this->toString());
 
-		if ($modification)
+		if (null !== $modification) {
 			return $child->modify($modification);
+		}
 
 		return $child;
 	}
 
 	/**
+	 * @param string $string
+	 * @return static
 	 * @throws WrongArgumentException
-	 * @return Date
-	**/
-	public function modify($string)
+	 */
+	public function modify(string $string): Date
 	{
 		try {
 			$this->dateTime->modify($string);
-		} catch (\Exception $e) {
-			throw new WrongArgumentException(
-				"wrong time string '{$string}'"
-			);
+		} catch (\Throwable $e) {
+			throw new WrongArgumentException("wrong time string '{$string}'");
 		}
 
 		return $this;
 	}
 
+	/**
+	 * @return false|int
+	 */
 	public function getDayStartStamp()
 	{
 		return
@@ -230,6 +282,9 @@ public function getDayStartStamp()
 			);
 	}
 
+	/**
+	 * @return false|int
+	 */
 	public function getDayEndStamp()
 	{
 		return
@@ -242,9 +297,11 @@ public function getDayEndStamp()
 	}
 
 	/**
+	 * @param int $weekStart
 	 * @return Date
-	**/
-	public function getFirstDayOfWeek($weekStart = Date::WEEKDAY_MONDAY)
+	 * @throws WrongArgumentException
+	 */
+	public function getFirstDayOfWeek(int $weekStart = Date::WEEKDAY_MONDAY): Date
 	{
 		return $this->spawn(
 			'-'.((7 + $this->getWeekDay() - $weekStart) % 7).' days'
@@ -252,43 +309,57 @@ public function getFirstDayOfWeek($weekStart = Date::WEEKDAY_MONDAY)
 	}
 
 	/**
+	 * @param int $weekStart
 	 * @return Date
-	**/
-	public function getLastDayOfWeek($weekStart = Date::WEEKDAY_MONDAY)
+	 * @throws WrongArgumentException
+	 */
+	public function getLastDayOfWeek(int $weekStart = Date::WEEKDAY_MONDAY): Date
 	{
 		return $this->spawn(
 			'+'.((13 - $this->getWeekDay() + $weekStart) % 7).' days'
 		);
 	}
 
-	public function toString()
+	/**
+	 * @return string
+	 */
+	public function toString(): string
 	{
 		return $this->dateTime->format(static::getFormat());
 	}
 
-	public function toFormatString($format)
+	/**
+	 * @param string $format
+	 * @return string
+	 */
+	public function toFormatString(string $format): string
 	{
 		return $this->dateTime->format($format);
 	}
 
-	public function toDialectString(Dialect $dialect)
+	/**
+	 * @param Dialect $dialect
+	 * @return string
+	 */
+	public function toDialectString(Dialect $dialect): string
 	{
-		// there are no known differences yet
 		return $dialect->quoteValue($this->toString());
 	}
 
 	/**
 	 * ISO 8601 date string
-	**/
-	public function toIsoString()
+	 * @return string
+	 */
+	public function toIsoString(): string
 	{
 		return $this->toString();
 	}
 
 	/**
 	 * @return Timestamp
-	**/
-	public function toTimestamp()
+	 * @throws WrongArgumentException
+	 */
+	public function toTimestamp(): Timestamp
 	{
 		return Timestamp::create($this->toStamp());
 	}
@@ -296,25 +367,29 @@ public function toTimestamp()
 	/**
 	 * @return DateTime|null
 	 */
-	public function getDateTime()
+	public function getDateTime(): ?DateTime
 	{
 		return $this->dateTime;
 	}
 
-	protected static function getFormat()
+	/**
+	 * @return string
+	 */
+	protected static function getFormat(): string
 	{
 		return 'Y-m-d';
 	}
 
-
+	/**
+	 * @param $date
+	 * @throws WrongArgumentException
+	 */
 	protected function import($date)
 	{
-		try{
+		try {
 			if (is_int($date) || is_numeric($date)) { // unix timestamp
-				$this->dateTime = new \DateTime(date(static::getFormat(), $date));
-
+				$this->dateTime = new DateTime(date(static::getFormat(), $date));
 			} elseif ($date && is_string($date)) {
-
 				if (
 					preg_match('/^(\d{1,4})[-\.](\d{1,2})[-\.](\d{1,2})/', $date, $matches)
 				) {
@@ -325,18 +400,14 @@ protected function import($date)
 					preg_match('/^(\d{1,2})[-\.](\d{1,2})[-\.](\d{1,4})/', $date, $matches)
 				) {
 					Assert::isTrue(
-						checkdate($matches[2], $matches[2], $matches[3])
+						checkdate($matches[2], $matches[1], $matches[3])
 					);
 				}
 
-				$this->dateTime = new \DateTime($date);
+				$this->dateTime = new DateTime($date);
 			}
-
-		} catch(\Exception $e) {
-			throw new WrongArgumentException(
-				"strange input given - '{$date}'"
-			);
+		} catch(\Throwable $e) {
+			throw new WrongArgumentException("strange input given - '{$date}'");
 		}
 	}
 }
-?>
diff --git a/src/Core/Base/Timestamp.php b/src/Core/Base/Timestamp.php
index 96cd7685ad..ff7d9d0f4c 100644
--- a/src/Core/Base/Timestamp.php
+++ b/src/Core/Base/Timestamp.php
@@ -12,72 +12,86 @@
 
 namespace OnPHP\Core\Base;
 
+use DateTimeZone;
+use OnPHP\Core\Exception\WrongArgumentException;
 use OnPHP\Core\Exception\WrongStateException;
 
-/* $Id$ */
-
 /**
  * Date and time container and utilities.
  *
  * @see Date
- *
  * @ingroup Base
-**/
+ */
 class Timestamp extends Date
 {
 	/**
+	 * @param $timestamp
+	 * @param DateTimeZone|null $zone
 	 * @return Timestamp
-	**/
-	public static function create($timestamp, \DateTimeZone $zone=null)
+	 * @throws WrongArgumentException
+	 */
+	public static function create($timestamp, DateTimeZone $zone = null): Timestamp
 	{
 		return new static($timestamp, $zone);
 	}
 
-	public static function now()
+	/**
+	 * @return string
+	 */
+	public static function now(): string
 	{
 		return date(static::getFormat());
 	}
 
 	/**
 	 * @return Timestamp
-	**/
-	public static function makeNow()
+	 * @throws WrongArgumentException
+	 */
+	public static function makeNow(): Timestamp
 	{
 		return new static(time());
 	}
 
 	/**
-	 * @return Timestamp
-	**/
-	public static function makeToday()
-	{
-		return new static(static::today());
-	}
-
-	public function __construct($dateTime, \DateTimeZone $zone=null)
+	 * @param $dateTime
+	 * @param DateTimeZone|null $zone
+	 * @throws WrongArgumentException
+	 */
+	public function __construct($dateTime, DateTimeZone $zone = null)
 	{
 		parent::__construct($dateTime);
 
-		if($zone) {
+		if (null !== $zone) {
 			$this->dateTime->setTimezone($zone);
 		}
-
 	}
 
-	private function getDefaultTimeZone()
+	/**
+	 * @return DateTimeZone
+	 * @throws WrongStateException
+	 */
+	private function getDefaultTimeZone(): DateTimeZone
 	{
 		try {
 			$defaultTimeZoneName = date_default_timezone_get();
-			return new \DateTimeZone($defaultTimeZoneName);
-		} catch(\Exception $e) {
+			return new DateTimeZone($defaultTimeZoneName);
+		} catch(\Throwable $e) {
 			throw new WrongStateException(
-				"strange default time zone given - '{$defaultTimeZoneName}'!".
-				'Use date_default_timezone_set() for set valid default time zone.'
+				(
+					($defaultTimeZoneName ?? false)
+						? "strange default time zone given - '{$defaultTimeZoneName}'!"
+						: "default time zone not fetched!"
+				) . ' Use date_default_timezone_set() for set valid default time zone.'
 			);
 		}
 	}
 
-	public function toTime($timeDelimiter = ':', $secondDelimiter = '.')
+	/**
+	 * @param string $timeDelimiter
+	 * @param string $secondDelimiter
+	 * @return string
+	 */
+	public function toTime(string $timeDelimiter = ':', string $secondDelimiter = '.'): string
 	{
 		return
 			$this->getHour()
@@ -87,33 +101,52 @@ public function toTime($timeDelimiter = ':', $secondDelimiter = '.')
 			.$this->getSecond();
 	}
 
+	/**
+	 * @param string $dateDelimiter
+	 * @param string $timeDelimiter
+	 * @param string $secondDelimiter
+	 * @return string
+	 */
 	public function toDateTime(
-		$dateDelimiter = '-',
-		$timeDelimiter = ':',
-		$secondDelimiter = '.'
-	)
+		string $dateDelimiter = '-',
+		string $timeDelimiter = ':',
+		string $secondDelimiter = '.'
+	): string
 	{
 		return
 			$this->toDate($dateDelimiter).' '
 			.$this->toTime($timeDelimiter, $secondDelimiter);
 	}
 
-	public function getHour()
+	/**
+	 * @return string
+	 */
+	public function getHour(): string
 	{
 		return $this->dateTime->format('H');
 	}
 
-	public function getMinute()
+	/**
+	 * @return string
+	 */
+	public function getMinute(): string
 	{
 		return $this->dateTime->format('i');
 	}
 
-	public function getSecond()
+	/**
+	 * @return string
+	 */
+	public function getSecond(): string
 	{
 		return $this->dateTime->format('s');
 	}
 
-	public function equals(Timestamp $timestamp)
+	/**
+	 * @param Timestamp $timestamp
+	 * @return bool
+	 */
+	public function equals(Timestamp $timestamp): bool
 	{
 		return ($this->toDateTime() === $timestamp->toDateTime());
 	}
@@ -126,10 +159,14 @@ public function getDayStartStamp()
 			return parent::getDayStartStamp();
 	}
 
+	/**
+	 * @return false|int
+	 */
 	public function getHourStartStamp()
 	{
-		if (!$this->getMinute() && !$this->getSecond())
+		if (!$this->getMinute() && !$this->getSecond()) {
 			return $this->dateTime->getTimestamp();
+		}
 
 		return
 			mktime(
@@ -144,8 +181,10 @@ public function getHourStartStamp()
 
 	/**
 	 * ISO 8601 time string
-	**/
-	public function toIsoString($convertToUtc = true)
+	 * @param bool $convertToUtc
+	 * @return string
+	 */
+	public function toIsoString(bool $convertToUtc = true): string
 	{
 		if ($convertToUtc)
 			return date('Y-m-d\TH:i:s\Z', $this->dateTime->getTimestamp() - date('Z', $this->dateTime->getTimestamp()));
@@ -155,15 +194,18 @@ public function toIsoString($convertToUtc = true)
 
 	/**
 	 * @return Timestamp
-	**/
-	public function toTimestamp()
+	 * @throws WrongArgumentException
+	 */
+	public function toTimestamp(): Timestamp
 	{
 		return $this->spawn();
 	}
 
-	protected static function getFormat()
+	/**
+	 * @return string
+	 */
+	protected static function getFormat(): string
 	{
 		return 'Y-m-d H:i:s';
 	}
-}
-?>
+}
\ No newline at end of file
diff --git a/src/Core/Base/TimestampTZ.php b/src/Core/Base/TimestampTZ.php
index 9f1593ea44..6b4965c7a7 100644
--- a/src/Core/Base/TimestampTZ.php
+++ b/src/Core/Base/TimestampTZ.php
@@ -10,8 +10,14 @@
 
 namespace OnPHP\Core\Base;
 
+use DateTimeZone;
+use OnPHP\Core\Exception\WrongArgumentException;
+
 /**
  * Timestamp with time zone
+ *
+ * @see Timestamp, Date
+ * @ingroup Base
  */
 class TimestampTZ extends Timestamp
 {
@@ -19,23 +25,24 @@ class TimestampTZ extends Timestamp
 	 * @static
 	 * @return string
 	 */
-	protected static function getFormat()
+	protected static function getFormat(): string
 	{
 		return 'Y-m-d H:i:sO';
 	}
 
 	/**
-	 * @return Timestamp
-	**/
-	public function toTimestamp($zone=null)
+	 * @param null $zone
+	 * @return Timestamp|TimestampTZ
+	 * @throws WrongArgumentException
+	 */
+	public function toTimestamp($zone = null): Timestamp
 	{
-		if($zone) {
-
+		if (null === $zone) {
 			if(
-				!($zone instanceof \DateTimeZone)
+				!($zone instanceof DateTimeZone)
 				&& is_scalar($zone)
 			) {
-				$zone = new \DateTimeZone($zone);
+				$zone = new DateTimeZone($zone);
 			}
 
 			return new static($this->toStamp(), $zone);
@@ -44,7 +51,13 @@ public function toTimestamp($zone=null)
 		return  parent::toTimestamp();
 	}
 
-	public static function compare(Date $left, Date $right)
+	/**
+	 * @param Date $left
+	 * @param Date $right
+	 * @return int
+	 * @throws WrongArgumentException
+	 */
+	public static function compare(Date $left, Date $right): int
 	{
 		Assert::isTrue(
 			(
@@ -55,5 +68,4 @@ public static function compare(Date $left, Date $right)
 
 		return parent::compare($left, $right);
 	}
-}
-?>
\ No newline at end of file
+}
\ No newline at end of file
diff --git a/src/Main/Base/CalendarDay.php b/src/Main/Base/CalendarDay.php
index 094d90c39a..60e0f3804a 100644
--- a/src/Main/Base/CalendarDay.php
+++ b/src/Main/Base/CalendarDay.php
@@ -26,7 +26,7 @@ final class CalendarDay extends Date
 	/**
 	 * @return CalendarDay
 	**/
-	public static function create($timestamp)
+	public static function create($timestamp): CalendarDay
 	{
 		return new self($timestamp);
 	}
diff --git a/src/Main/Base/DateRange.php b/src/Main/Base/DateRange.php
index f441677770..d17a5156d0 100644
--- a/src/Main/Base/DateRange.php
+++ b/src/Main/Base/DateRange.php
@@ -23,55 +23,158 @@
  * 
  * @see Date
  * @see TimestampRange
- * 
  * @ingroup Helpers
 **/
 class DateRange implements Stringable, SingleRange
 {
-	private $start	= null;
-	private $end	= null;
+	/**
+	 * @var Date|null
+	 */
+	private ?Date $start	= null;
+	/**
+	 * @var Date|null
+	 */
+	private ?Date $end      = null;
+	/**
+	 * @var int|null
+	 */
+	private ?int $dayStartStamp	= null;
+	/**
+	 * @var int|null
+	 */
+	private ?int $dayEndStamp	= null;
 
-	private $dayStartStamp	= null;
-	private $dayEndStamp	= null;
+	/**
+	 * @param Date|null $start
+	 * @param Date|null $end
+	 * @return static
+	 * @throws WrongArgumentException
+	 */
+	public static function create(Date $start = null, Date $end = null): DateRange
+	{
+		return new static($start, $end);
+	}
 
 	/**
-	 * @return DateRange
-	**/
-	public static function create($start = null, $end = null)
+	 * @param DateRange[] $array
+	 * @return DateRange[]
+	 * @throws WrongArgumentException
+	 */
+	public static function merge(array $array): array
 	{
-		return new self($start, $end);
+		array_map(function ($item) {
+			Assert::isInstance($item, DateRange::class);
+			Assert::isTrue(!$item->isOpen());
+		}, $array);
+
+		$out = array();
+
+		foreach ($array as $range) {
+			$accepted = false;
+
+			foreach ($out as $outRange) {
+				if ($outRange->isNeighbour($range)) {
+					$outRange->enlarge($range);
+					$accepted = true;
+				}
+			}
+
+			if (!$accepted) {
+				$out[] = clone $range;
+			}
+		}
+
+		return $out;
+	}
+
+	/**
+	 * @param DateRange $left
+	 * @param DateRange $right
+	 * @return int
+	 */
+	public static function compare(DateRange $left, DateRange $right): int
+	{
+		if ($left->isEmpty() && $right->isEmpty()) {
+			return 0;
+		} elseif ($left->isEmpty()) {
+			return 1;
+		} elseif ($right->isEmpty()) {
+			return -1;
+		}
+
+		$leftStart = $left->getStartStamp();
+		$leftEnd = $left->getEndStamp();
+
+		$rightStart = $right->getStartStamp();
+		$rightEnd = $right->getEndStamp();
+
+		if (
+			!$leftStart && !$rightStart
+			|| $leftStart && $rightStart && ($leftStart == $rightStart)
+		) {
+			if (
+				!$leftEnd && !$rightEnd
+				|| $leftEnd && $rightEnd && ($leftEnd == $rightEnd)
+			) {
+				return 0;
+			} elseif (
+				$leftEnd && !$rightEnd
+				|| $leftEnd < $rightEnd
+			) {
+				return -1;
+			}
+
+			return 1;
+		} elseif (
+			!$leftStart && $rightStart
+			|| $leftStart < $rightStart
+		) {
+			return -1;
+		} elseif ($leftStart && !$rightStart) {
+			return 1;
+		}
+
+		return 1;
 	}
 
-	public function __construct($start = null, $end = null)
+	/**
+	 * @param Date|null $start
+	 * @param Date|null $end
+	 * @throws WrongArgumentException
+	 */
+	public function __construct(Date $start = null, Date $end = null)
 	{
-		if ($start)
+		if ($start instanceof Date) {
 			$this->setStart($start);
+		}
 
-		if ($end)
+		if ($end instanceof Date) {
 			$this->setEnd($end);
+		}
 	}
 
 	public function __clone()
 	{
-		if ($this->start)
+		if ($this->start) {
 			$this->start = clone $this->start;
+		}
 
-		if ($this->end)
+		if ($this->end) {
 			$this->end = clone $this->end;
+		}
 	}
 
 	/**
+	 * @param Date $start
+	 * @return static
 	 * @throws WrongArgumentException
-	 * @return DateRange
-	**/
-	public function setStart(/* Date */ $start)
+	 */
+	public function setStart(Date $start): DateRange
 	{
-		$this->checkType($start);
-
-		if ($this->end && $this->end->toStamp() < $start->toStamp())
-			throw new WrongArgumentException(
-				'start must be lower than end'
-			);
+		Assert::isFalse(
+		$this->end instanceof Date && $this->end->toStamp() < $start->toStamp(),
+		'start must be lower than end'
+		);
 
 		$this->start = $start;
 		$this->dayStartStamp = null;
@@ -80,106 +183,123 @@ public function setStart(/* Date */ $start)
 	}
 
 	/**
-	 * @return DateRange
-	**/
-	public function safeSetStart(/* Date */ $start)
+	 * @param Date $start
+	 * @return static
+	 * @throws WrongArgumentException
+	 */
+	public function safeSetStart(Date $start): DateRange
 	{
-		if (
-			!$this->getEnd()
-			|| Timestamp::compare(
-				$start, $this->getEnd()
-			) < 0
-		)
+		if (!$this->getEnd() instanceof Date) {
 			$this->setStart($start);
+			return $this;
+		}
 
-		elseif ($this->getEnd())
-			$this->setStart($this->getEnd());
+		$this->setStart(
+			Timestamp::compare($start, $this->getEnd()) < 0
+				? $start
+				: $this->getEnd()
+		);
 
 		return $this;
 	}
 
 	/**
-	 * @return DateRange
-	**/
-	public function safeSetEnd(/* Date */ $end)
+	 * @param Date $end
+	 * @return static
+	 * @throws WrongArgumentException
+	 */
+	public function safeSetEnd(Date $end): DateRange
 	{
-		if (
-			!$this->getStart()
-			|| Timestamp::compare(
-				$end, $this->getStart()
-			) > 0
-		)
+		if (!$this->getStart() instanceof Date) {
 			$this->setEnd($end);
+			return $this;
+		}
 
-		elseif ($this->getStart())
-			$this->setEnd($this->getStart());
+		$this->setEnd(
+			Timestamp::compare($end, $this->getStart()) > 0
+				? $end
+				: $this->getStart()
+		);
 
 		return $this;
 	}
 
 	/**
+	 * @param Date $end
+	 * @return static
 	 * @throws WrongArgumentException
-	 * @return DateRange
-	**/
-	public function setEnd(/* Date */ $end)
+	 */
+	public function setEnd(Date $end): DateRange
 	{
-		$this->checkType($end);
-
-		if ($this->start && $this->start->toStamp() > $end->toStamp())
-			throw new WrongArgumentException(
-				'end must be higher than start'
-			);
+		Assert::isFalse(
+			$this->start instanceof Date && $this->start->toStamp() > $end->toStamp(),
+			'end must be higher than start'
+		);
 
 		$this->end = $end;
 		$this->dayEndStamp = null;
+
 		return $this;
 	}
 
 	/**
-	 * @return DateRange
-	**/
-	public function lazySet($start = null, $end = null)
+	 * @param Date|null $start
+	 * @param Date|null $end
+	 * @return static
+	 * @throws WrongArgumentException
+	 */
+	public function lazySet(Date $start = null, Date $end = null): DateRange
 	{
-		if ($start)
-			$this->checkType($start);
-
-		if ($end)
-			$this->checkType($end);
-
-		if ($start && $end) {
-			if ($start->toStamp() >= $end->toStamp())
+		if (
+			$start instanceof Date
+			&& $end instanceof Date
+		) {
+			if ($start->toStamp() >= $end->toStamp()) {
 				$this->setEnd($start)->setStart($end);
-			else
+			} else {
 				$this->setStart($start)->setEnd($end);
-		} elseif ($start)
+			}
+
+			return $this;
+		}
+
+		if ($start instanceof Date) {
 			$this->setStart($start);
-		elseif ($end)
+		}
+
+		if ($end instanceof Date) {
 			$this->setEnd($end);
+		}
 
 		return $this;
 	}
 
 	/**
-	 * @return DateRange
-	**/
-	public function dropStart()
+	 * @return static
+	 */
+	public function dropStart(): DateRange
 	{
 		$this->start = null;
 		$this->dayStartStamp = null;
+
 		return $this;
 	}
 
 	/**
-	 * @return DateRange
-	**/
-	public function dropEnd()
+	 * @return static
+	 */
+	public function dropEnd(): DateRange
 	{
 		$this->end = null;
 		$this->dayEndStamp = null;
+
 		return $this;
 	}
 
-	public function isEmpty()
+	/**
+	 * @return bool
+	 */
+	public function isEmpty(): bool
 	{
 		return
 			($this->start === null)
@@ -187,55 +307,80 @@ public function isEmpty()
 	}
 
 	/**
-	 * @return Date
-	**/
-	public function getStart()
+	 * @return Date|null
+	 */
+	public function getStart(): ?Date
 	{
 		return $this->start;
 	}
 
 	/**
-	 * @return Date
-	**/
-	public function getEnd()
+	 * @return Date|null
+	 */
+	public function getEnd(): ?Date
 	{
 		return $this->end;
 	}
 
-	public function toDateString(
-		$internalDelimiter = '-',
-		$dateDelimiter = ' - '
-	)
+	/**
+	 * @param string $internalDelimiter
+	 * @param string $dateDelimiter
+	 * @return string|null
+	 */
+	public function toDateString(string $internalDelimiter = '-', string $dateDelimiter = ' - '): ?string
 	{
-		if ($this->start && $this->end)
-			return
-				"{$this->start->toDate($internalDelimiter)}"
-				.$dateDelimiter
-				."{$this->end->toDate($internalDelimiter)}";
-		elseif ($this->start)
+		if (
+			$this->start instanceof Date
+			&& $this->end instanceof Date
+		) {
+			return $this->start->toDate($internalDelimiter)
+				. $dateDelimiter
+				. $this->end->toDate($internalDelimiter);
+		}
+
+		if ($this->start instanceof Date) {
 			return $this->start->toDate($internalDelimiter);
-		elseif ($this->end)
+		}
+
+		if ($this->end instanceof Date) {
 			return $this->end->toDate($internalDelimiter);
+		}
 
 		return null;
 	}
 
-	public function toString($delimiter = ' - ')
+	/**
+	 * @param string $delimiter
+	 * @return string|null
+	 */
+	public function toString(string $delimiter = ' - '): ?string
 	{
-		if ($this->start && $this->end)
+		if (
+			$this->start instanceof Date
+			&& $this->end instanceof Date
+		) {
 			return
 				$this->start->toString()
-				.$delimiter
-				.$this->end->toString();
-		elseif ($this->start)
+				. $delimiter
+				. $this->end->toString();
+		}
+
+		if ($this->start instanceof Date) {
 			return $this->start->toString();
-		elseif ($this->end)
+		}
+
+		if ($this->end instanceof Date) {
 			return $this->end->toString();
+		}
 
 		return null;
 	}
 
-	public function overlaps(DateRange $range)
+	/**
+	 * @param DateRange $range
+	 * @return bool
+	 */
+	public function overlaps(DateRange $range): bool
 	{
 		if ($this->isEmpty() || $range->isEmpty())
 			return true;
@@ -245,51 +390,28 @@ public function overlaps(DateRange $range)
 		$min = $range->getStartStamp();
 		$max = $range->getEndStamp();
 
-		return (
+		return
 			(
-				$min
-				&& $max
-				&& (
-					(
-						$left
-						&& $right
-						&& (
+				$min && $max && (
+					( $left && $right && (
 							(($left <= $min) && ($min <= $right))
 							|| (($min <= $left) && ($left <= $max))
 						)
-					) || (
-						!$left
-						&& ($min <= $right)
-					) || (
-						!$right
-						&& ($left <= $max)
-					)
-				)
-			) || (
-				$min
-				&& !$max
-				&& (
-					!$right
-					|| (
-						$right
-						&& ($min <= $right)
-					)
-				)
-			) || (
-				!$min
-				&& $max
-				&& (
-					!$left
-					|| (
-						$left
-						&& ($left <= $max)
 					)
+					|| ( !$left && ($min <= $right) ) || ( !$right && ($left <= $max) )
 				)
 			)
-		);
+			|| ( $min && !$max && ( !$right || ($min <= $right) ) )
+			|| ( !$min && $max && ( !$left || ($left <= $max) ) )
+		;
 	}
 
-	public function contains(/* Timestamp */ $date)
+	/**
+	 * @param Date $date
+	 * @return bool
+	 * @throws WrongArgumentException
+	 */
+	public function contains(object $date): bool
 	{
 		$this->checkType($date);
 
@@ -297,28 +419,24 @@ public function contains(/* Timestamp */ $date)
 		$end = $this->getEndStamp();
 		$probe = $date->toStamp();
 
-		if (
-			(!$start && !$end)
-			|| (!$start && $end >= $probe)
-			|| (!$end && $start <= $probe)
+		return
+			(null === $start && null === $end)
+			|| (null === $start && $end >= $probe)
+			|| (null === $end && $start <= $probe)
 			|| ($start <= $probe && $end >= $probe)
-		)
-			return true;
-
-		return false;
+		;
 	}
 
-	public function split()
+	/**
+	 * @return Date[]
+	 * @throws WrongArgumentException
+	 */
+	public function split(): array
 	{
-		Assert::isFalse(
-			$this->isOpen(),
-			"open range can't be splitted"
-		);
+		Assert::isFalse($this->isOpen(), "can't split open range");
 
 		$dates = array();
-
 		$start = new Date($this->start->getDayStartStamp());
-
 		$endStamp = $this->end->getDayEndStamp();
 
 		for (
@@ -332,31 +450,16 @@ public function split()
 		return $dates;
 	}
 
-	public static function merge($array /* of DateRanges */)
-	{
-		$out = array();
-
-		foreach ($array as $range) {
-			$accepted = false;
-
-			foreach ($out as $outRange)
-				if ($outRange->isNeighbour($range)) {
-					$outRange->enlarge($range);
-					$accepted = true;
-				}
-
-			if (!$accepted)
-				$out[] = clone $range;
-		}
-
-		return $out;
-	}
-
-	public function isNeighbour(DateRange $range)
+	/**
+	 * @param DateRange $range
+	 * @return bool
+	 * @throws WrongArgumentException
+	 */
+	public function isNeighbour(DateRange $range): bool
 	{
 		Assert::isTrue(!$this->isOpen() && !$range->isOpen());
 
-		if (
+		return
 			$this->overlaps($range)
 			|| (
 				$this->start->spawn('-1 day')->getDayStartStamp()
@@ -365,112 +468,98 @@ public function isNeighbour(DateRange $range)
 				$this->end->spawn('+1 day')->getDayStartStamp()
 				== $range->start->getDayStartStamp()
 			)
-		)
-			return true;
-
-		return false;
+		;
 	}
 
-	public function isOpen()
+	/**
+	 * @return bool
+	 */
+	public function isOpen(): bool
 	{
-		return !$this->start || !$this->end;
+		return
+			!$this->start instanceof Date
+			|| !$this->end instanceof Date;
 	}
 
 	/**
 	 * enlarges $this by given $range, if last one is wider
-	 * 
-	 * @return DateRange
-	**/
-	public function enlarge(DateRange $range)
+	 * NB! Be careful if DateRange 01 Mar 2000 - 31 Mar 2000
+	 * enlarge with DateRange 01 Jan 2000 - 31 Jan 2000 new
+	 * DateRange will be 01 Jan 2000 - 31 Mar 2000. Will be
+	 * included center range 01 Feb 2000 - 28 Feb 2000
+	 * @param DateRange $range
+	 * @return static
+	 * @throws WrongArgumentException
+	 */
+	public function enlarge(DateRange $range): DateRange
 	{
-		if (!$range->start)
-			$this->start = null;
-		elseif (
-			$this->start
+		if (!$range->start instanceof Date) {
+			$this->dropStart();
+		} elseif (
+			$this->start instanceof Date
 			&& $this->start->toStamp() > $range->start->toStamp()
-		)
-			$this->start = clone $range->start;
+		) {
+			$this->setStart(clone $range->start);
+		}
 
-		if (!$range->end)
-			$this->end = null;
-		elseif (
-			$this->end
+		if (!$range->end instanceof Date) {
+			$this->dropEnd();
+		} elseif (
+			$this->end instanceof Date
 			&& $this->end->toStamp() < $range->end->toStamp()
-		)
-			$this->end = clone $range->end;
+		) {
+			$this->setEnd(clone $range->end);
+		}
 
 		return $this;
 	}
 
 	/**
 	 * intersection of $this and given $range
-	 * 
-	 * @return DateRange
-	**/
-	public function clip(DateRange $range)
+	 * @return static
+	 * @throws WrongArgumentException
+	 */
+	public function clip(DateRange $range): DateRange
 	{
 		Assert::isTrue($this->overlaps($range));
 
 		if (
-			$range->start
+			$range->start instanceof Date
 			&& (
-				$this->start
-				&& $range->start->toStamp() > $this->start->toStamp()
-				|| !$this->start
+				!$this->start instanceof Date
+				|| $range->start->toStamp() > $this->start->toStamp()
 			)
-		)
+		) {
 			$this->start = clone $range->start;
+		}
 
 		if (
-			$range->end
+			$range->end instanceof Date
 			&& (
-				$this->end
-				&& $range->end->toStamp() < $this->end->toStamp()
-				|| !$this->end
+				!$this->end instanceof Date
+				|| $range->end->toStamp() < $this->end->toStamp()
 			)
-		)
+		) {
 			$this->end = clone $range->end;
+		}
 
 		return $this;
 	}
 
 	/**
-	 * result is read-only, no error checking
-	 * 
-	 * @return DateRange
-	**/
-	public function lightCopyOnClip(DateRange $range)
+	 * @param DateRange $range
+	 * @return static
+	 * @throws WrongArgumentException
+	 */
+	public function lightCopyOnClip(DateRange $range): DateRange
 	{
-		$copy = DateRange::create();
-
-		if (
-			$range->start
-			&& (
-				$this->start
-				&& $range->start->toStamp() > $this->start->toStamp()
-				|| !$this->start
-			)
-		)
-			$copy->start = $range->start;
-		else
-			$copy->start = $this->start;
-
-		if (
-			$range->end
-			&& (
-				$this->end
-				&& $range->end->toStamp() < $this->end->toStamp()
-				|| !$this->end
-			)
-		)
-			$copy->end = $range->end;
-		else
-			$copy->end = $this->end;
-
-		return $copy;
+		return (clone $this)->clip($range);
 	}
 
-	public function getStartStamp() // null if start is null
+	/**
+	 * @return int|null
+	 */
+	public function getStartStamp(): ?int
 	{
 		if ($this->start) {
 			if (!$this->dayStartStamp) {
@@ -483,7 +572,10 @@ public function getStartStamp() // null if start is null
 		return null;
 	}
 
-	public function getEndStamp() // null if end is null
+	/**
+	 * @return int|null
+	 */
+	public function getEndStamp(): ?int
 	{
 		if ($this->end) {
 			if (!$this->dayEndStamp) {
@@ -496,76 +588,45 @@ public function getEndStamp() // null if end is null
 		return null;
 	}
 
-	public static function compare(DateRange $left, DateRange $right)
-	{
-		if ($left->isEmpty() && $right->isEmpty())
-			return 0;
-		elseif ($left->isEmpty())
-			return 1;
-		elseif ($right->isEmpty())
-			return -1;
-
-		$leftStart = $left->getStartStamp();
-		$leftEnd = $left->getEndStamp();
-
-		$rightStart = $right->getStartStamp();
-		$rightEnd = $right->getEndStamp();
-
-		if (
-			!$leftStart && !$rightStart
-			|| $leftStart && $rightStart && ($leftStart == $rightStart)
-		) {
-			if (
-				!$leftEnd && !$rightEnd
-				|| $leftEnd && $rightEnd && ($leftEnd == $rightEnd)
-			)
-				return 0;
-			elseif (!$leftEnd && $rightEnd)
-				return 1;
-			elseif ($leftEnd && !$rightEnd)
-				return -1;
-			elseif ($leftEnd < $rightEnd)
-				return -1;
-			else
-				return 1;
-		} elseif (!$leftStart && $rightStart)
-			return -1;
-		elseif ($leftStart && !$rightStart)
-			return 1;
-		elseif ($leftStart < $rightStart)
-			return -1;
-		else
-			return 1;
-	}
-
-	public function isOneDay()
+	/**
+	 * @return bool
+	 */
+	public function isOneDay(): bool
 	{
-		return (!$this->isOpen())
-			&& ($this->start->toDate() == $this->end->toDate());
+		return
+			!$this->isOpen()
+			&& $this->start->toDate() == $this->end->toDate();
 	}
 
 	/**
 	 * @return TimestampRange
-	**/
-	public function toTimestampRange()
+	 * @throws WrongArgumentException
+	 */
+	public function toTimestampRange(): TimestampRange
 	{
 		return
 			TimestampRange::create(
-				$this->getStart()->toTimestamp(),
-				$this->getEnd()->toTimestamp()
+				$this->getStart() ? $this->getStart()->toTimestamp() : null,
+				$this->getEnd() ? $this->getEnd()->toTimestamp() : null
 			);
 	}
 
-	protected function checkType($value)
+	/**
+	 * @param $value
+	 * @throws WrongArgumentException
+	 */
+	protected function checkType($value): void
 	{
 		Assert::isTrue(
 			ClassUtils::isInstanceOf($value, $this->getObjectName())
 		);
 	}
 
-	protected function getObjectName()
+	/**
+	 * @return string
+	 */
+	protected function getObjectName(): string
 	{
 		return Date::class;
 	}
-}
-?>
+}
\ No newline at end of file
diff --git a/src/Main/Base/SingleRange.php b/src/Main/Base/SingleRange.php
index 377e01ab4b..ee870f123a 100644
--- a/src/Main/Base/SingleRange.php
+++ b/src/Main/Base/SingleRange.php
@@ -16,9 +16,8 @@
 **/
 interface SingleRange
 {
-	public function getStart();
-	public function getEnd();
+	public function getStart(): ?object;
+	public function getEnd(): ?object;
 
-	public function contains($probe);
-}
-?>
\ No newline at end of file
+	public function contains(object $probe): bool;
+}
\ No newline at end of file
diff --git a/src/Main/Base/TimestampRange.php b/src/Main/Base/TimestampRange.php
index 03cbfc0ba5..799d92b9b8 100644
--- a/src/Main/Base/TimestampRange.php
+++ b/src/Main/Base/TimestampRange.php
@@ -19,15 +19,7 @@
 **/
 class TimestampRange extends DateRange
 {
-	/**
-	 * @return TimestampRange
-	**/
-	public static function create($start = null, $end = null)
-	{
-		return new self($start, $end);
-	}
-
-	public function getStartStamp() // null if start is null
+	public function getStartStamp(): ?int // null if start is null
 	{
 		if ($start = $this->getStart()) {
 			return $start->toStamp();
@@ -36,7 +28,7 @@ public function getStartStamp() // null if start is null
 		return null;
 	}
 
-	public function getEndStamp() // null if end is null
+	public function getEndStamp(): ?int // null if end is null
 	{
 		if ($end = $this->getEnd()) {
 			return $end->toStamp();
@@ -46,16 +38,18 @@ public function getEndStamp() // null if end is null
 	}
 
 	/**
-	 * @return TimestampRange
-	**/
-	public function toTimestampRange()
+	 * @return static
+	 */
+	public function toTimestampRange(): TimestampRange
 	{
 		return $this;
 	}
 
-	protected function getObjectName()
+	/**
+	 * @return string
+	 */
+	protected function getObjectName(): string
 	{
-		return '\OnPHP\Core\Base\Timestamp';
+		return Timestamp::class;
 	}
-}
-?>
\ No newline at end of file
+}
\ No newline at end of file
diff --git a/src/Main/Net/Ip/IpNetwork.php b/src/Main/Net/Ip/IpNetwork.php
index 12563fb499..5682ad8d40 100644
--- a/src/Main/Net/Ip/IpNetwork.php
+++ b/src/Main/Net/Ip/IpNetwork.php
@@ -61,7 +61,7 @@ public function getMask()
 	/**
 	 * @return IpAddress
 	**/
-	public function getStart()
+	public function getStart(): ?IpAddress
 	{
 		return $this->ip;
 	}
@@ -69,7 +69,7 @@ public function getStart()
 	/**
 	 * @return IpAddress
 	**/
-	public function getEnd()
+	public function getEnd(): ?IpAddress
 	{
 		if (!$this->end) {
 			$this->end =
@@ -81,7 +81,12 @@ public function getEnd()
 		return $this->end;
 	}
 
-	public function contains(/* IpAddress */ $probe)
+	/**
+	 * @param IpAddress $probe
+	 * @return bool
+	 * @throws WrongArgumentException
+	 */
+	public function contains(object $probe): bool
 	{
 		Assert::isInstance($probe, IpAddress::class);
 
diff --git a/src/Main/Net/Ip/IpRange.php b/src/Main/Net/Ip/IpRange.php
index f2131f777a..36b8fdad39 100644
--- a/src/Main/Net/Ip/IpRange.php
+++ b/src/Main/Net/Ip/IpRange.php
@@ -64,7 +64,7 @@ public function __construct(/**/)
 	/**
 	 * @return IpAddress
 	**/
-	public function getStart()
+	public function getStart(): ?IpAddress
 	{
 		return $this->startIp;
 	}
@@ -82,7 +82,7 @@ public function setStart(IpAddress $startIp)
 	/**
 	 * @return IpAddress
 	**/
-	public function getEnd()
+	public function getEnd(): ?IpAddress
 	{
 		return $this->endIp;
 	}
@@ -97,7 +97,12 @@ public function setEnd(IpAddress $endIp)
 		return $this;
 	}
 
-	public function contains(/* IpAddress */ $probe)
+	/**
+	 * @param IpAddress $probe
+	 * @return bool
+	 * @throws WrongArgumentException
+	 */
+	public function contains(object $probe): bool
 	{
 		Assert::isInstance($probe, IpAddress::class);
 
diff --git a/src/Meta/Builder/BusinessClassBuilder.php b/src/Meta/Builder/BusinessClassBuilder.php
index 749a506be5..c5ba7d7da9 100644
--- a/src/Meta/Builder/BusinessClassBuilder.php
+++ b/src/Meta/Builder/BusinessClassBuilder.php
@@ -79,7 +79,7 @@ public static function dao()
 EOT;
 
 			if (!$type || $type->getId() !== MetaClassType::CLASS_ABSTRACT) {
-				$customCreate = null;
+				$buildCreate = true;
 				
 				if (
 					$class->getFinalParent()->getPattern()
@@ -90,55 +90,22 @@ public static function dao()
 					while ($parent = $parent->getParent()) {
 						$info = new \ReflectionClass($parent->getNameWithNS());
 						
-						if (
-							$info->hasMethod('create')
-							&& ($info->getMethod('create')->getParameters() > 0)
-						) {
-							$customCreate = true;
+						if ($info->hasMethod('create')) {
+							$buildCreate = false;
 							break;
 						}
 					}
 				}
 				
-				if ($customCreate) {
-					$creator = $info->getMethod('create');
-					
-					$declaration = array();
-					
-					foreach ($creator->getParameters() as $parameter) {
-						$declaration[] =
-							'$'.$parameter->getName()
-							// no one can live without default value @ ::create
-							.' = '
-							.(
-								$parameter->getDefaultValue()
-									? $parameter->getDefaultValue()
-									: 'null'
-							);
-					}
-					
-					$declaration = implode(', ', $declaration);
-					
-					$out .= <<<EOT
-
-	/**
-	 * @return {$class->getName()}
-	**/
-	public static function create({$declaration})
-	{
-		return new self({$declaration});
-	}
-		
-EOT;
-				} else {
+				if ($buildCreate) {
 					$out .= <<<EOT
 
 	/**
-	 * @return {$class->getName()}
+	 * @return static
 	**/
-	public static function create()
+	public static function create(): {$class->getName()}
 	{
-		return new self;
+		return new static;
 	}
 		
 EOT;
diff --git a/tests/Core/DateRangeTest.php b/tests/Core/DateRangeTest.php
index 173cf85248..17775e91c3 100644
--- a/tests/Core/DateRangeTest.php
+++ b/tests/Core/DateRangeTest.php
@@ -3,7 +3,10 @@
 namespace OnPHP\Tests\Core;
 
 use OnPHP\Core\Base\Date;
+use OnPHP\Core\Base\Timestamp;
+use OnPHP\Core\Exception\WrongArgumentException;
 use OnPHP\Main\Base\DateRange;
+use OnPHP\Main\Base\TimestampRange;
 use OnPHP\Tests\TestEnvironment\TestCase;
 
 /**
@@ -12,6 +15,799 @@
  */
 final class DateRangeTest extends TestCase
 {
+	public function testCreate()
+	{
+		$dateRange = DateRange::create();
+		$this->assertInstanceOf(DateRange::class, $dateRange);
+		$this->assertNull($dateRange->getStart());
+		$this->assertNull($dateRange->getEnd());
+
+		$date = Date::create('2007-01-01');
+		$dateRange = DateRange::create($date);
+		$this->assertInstanceOf(DateRange::class, $dateRange);
+		$this->assertInstanceOf(Date::class, $dateRange->getStart());
+		$this->assertEquals($date->toDate(), $dateRange->getStart()->toDate());
+		$this->assertNull($dateRange->getEnd());
+
+		$date = Date::create('2008-01-01');
+		$dateRange = DateRange::create(null, $date);
+		$this->assertInstanceOf(DateRange::class, $dateRange);
+		$this->assertNull($dateRange->getStart());
+		$this->assertInstanceOf(Date::class, $dateRange->getEnd());
+		$this->assertEquals($date->toDate(), $dateRange->getEnd()->toDate());
+
+		$start = Date::create('2007-01-01');
+		$end = Date::create('2008-01-01');
+		$dateRange = DateRange::create($start, $end);
+		$this->assertInstanceOf(DateRange::class, $dateRange);
+		$this->assertInstanceOf(Date::class, $dateRange->getStart());
+		$this->assertInstanceOf(Date::class, $dateRange->getEnd());
+		$this->assertEquals($start->toDate(), $dateRange->getStart()->toDate());
+		$this->assertEquals($end->toDate(), $dateRange->getEnd()->toDate());
+
+		$start = Date::create('2007-01-01');
+		$end = Date::create('2008-01-01');
+		try {
+			DateRange::create($end, $start);
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+	}
+
+	public function testMerge()
+	{
+		try {
+			DateRange::merge([DateRange::create()]);
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+		try {
+			DateRange::merge([DateRange::create(Date::create('2007-01-01'))]);
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+		try {
+			DateRange::merge([DateRange::create(null, Date::create('2007-12-31'))]);
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+		try {
+			DateRange::merge([
+				DateRange::create(Date::create('2007-01-01'), Date::create('2007-12-31')),
+				DateRange::create()
+			]);
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+
+		$output = DateRange::merge([DateRange::create(Date::create('2007-01-01'), Date::create('2007-12-31'))]);
+		$this->assertCount(1, $output);
+
+		$output = DateRange::merge([
+			DateRange::create(Date::create('2007-01-01'), Date::create('2007-01-31')),
+			DateRange::create(Date::create('2007-03-01'), Date::create('2007-03-31')),
+			DateRange::create(Date::create('2007-05-01'), Date::create('2007-05-31')),
+		]);
+		$this->assertCount(3, $output);
+
+		$output = DateRange::merge([
+			DateRange::create(Date::create('2007-01-01'), Date::create('2007-01-31')),
+			DateRange::create(Date::create('2007-02-20'), Date::create('2007-02-28')),
+			DateRange::create(Date::create('2007-05-01'), Date::create('2007-05-31')),
+			DateRange::create(Date::create('2007-03-01'), Date::create('2007-03-31')),
+		]);
+		$this->assertCount(3, $output);
+		$this->assertEquals($output[0]->getStart()->toDate(), Date::create('2007-01-01')->toDate());
+		$this->assertEquals($output[0]->getEnd()->toDate(), Date::create('2007-01-31')->toDate());
+		$this->assertEquals($output[1]->getStart()->toDate(), Date::create('2007-02-20')->toDate());
+		$this->assertEquals($output[1]->getEnd()->toDate(), Date::create('2007-03-31')->toDate());
+		$this->assertEquals($output[2]->getStart()->toDate(), Date::create('2007-05-01')->toDate());
+		$this->assertEquals($output[2]->getEnd()->toDate(), Date::create('2007-05-31')->toDate());
+
+		$output = DateRange::merge([
+			DateRange::create(Date::create('2007-01-01'), Date::create('2007-01-31')),
+			DateRange::create(Date::create('2007-02-20'), Date::create('2007-02-28')),
+			DateRange::create(Date::create('2007-04-01'), Date::create('2007-04-30')),
+			DateRange::create(Date::create('2007-05-01'), Date::create('2007-05-31')),
+			DateRange::create(Date::create('2007-03-01'), Date::create('2007-03-31')),
+		]);
+		$this->assertCount(3, $output);
+		$this->assertEquals($output[0]->getStart()->toDate(), Date::create('2007-01-01')->toDate());
+		$this->assertEquals($output[0]->getEnd()->toDate(), Date::create('2007-01-31')->toDate());
+		$this->assertEquals($output[1]->getStart()->toDate(), Date::create('2007-02-20')->toDate());
+		$this->assertEquals($output[1]->getEnd()->toDate(), Date::create('2007-03-31')->toDate());
+		$this->assertEquals($output[2]->getStart()->toDate(), Date::create('2007-03-01')->toDate());
+		$this->assertEquals($output[2]->getEnd()->toDate(), Date::create('2007-05-31')->toDate());
+	}
+
+	public function testCompare()
+	{
+		$this->assertEquals(0,
+			DateRange::compare(
+				DateRange::create(), DateRange::create()
+			)
+		);
+		$this->assertEquals(1,
+			DateRange::compare(
+				DateRange::create(),
+				DateRange::create(Date::makeToday())
+			)
+		);
+		$this->assertEquals(1,
+			DateRange::compare(
+				DateRange::create(),
+				DateRange::create(null, Date::makeToday())
+			)
+		);
+		$this->assertEquals(1,
+			DateRange::compare(
+				DateRange::create(),
+				DateRange::create(Date::makeToday(), Date::create("+1 week"))
+			)
+		);
+		$this->assertEquals(-1,
+			DateRange::compare(
+				DateRange::create(Date::makeToday()),
+				DateRange::create()
+			)
+		);
+		$this->assertEquals(-1,
+			DateRange::compare(
+				DateRange::create(null, Date::makeToday()),
+				DateRange::create()
+			)
+		);
+		$this->assertEquals(-1,
+			DateRange::compare(
+				DateRange::create(Date::makeToday(), Date::create("+1 week")),
+				DateRange::create()
+			)
+		);
+
+		$this->assertEquals(1,
+			DateRange::compare(
+				DateRange::create(null, Date::create('2006-01-01')),
+				DateRange::create(null, Date::create('2005-01-01'))
+			)
+		);
+		$this->assertEquals(0,
+			DateRange::compare(
+				DateRange::create(null, Date::create('2006-01-01')),
+				DateRange::create(null, Date::create('2006-01-01'))
+			)
+		);
+		$this->assertEquals(-1,
+			DateRange::compare(
+				DateRange::create(null, Date::create('2006-01-01')),
+				DateRange::create(null, Date::create('2007-01-01'))
+			)
+		);
+		$this->assertEquals(-1,
+			DateRange::compare(
+				DateRange::create(null, Date::create('2006-01-01')),
+				DateRange::create(Date::create('2007-01-01'))
+			)
+		);
+		$this->assertEquals(0,
+			DateRange::compare(
+				DateRange::create(null, Date::create('2006-01-01')),
+				DateRange::create(null, Date::create('2006-01-01'))
+			)
+		);
+		$this->assertEquals(1,
+			DateRange::compare(
+				DateRange::create(null, Date::create('2006-01-01')),
+				DateRange::create(null, Date::create('2005-01-01'))
+			)
+		);
+
+		$this->assertEquals(1,
+			DateRange::compare(
+				DateRange::create(Date::create('2006-01-01')),
+				DateRange::create(null, Date::create('2005-01-01'))
+			)
+		);
+		$this->assertEquals(1,
+			DateRange::compare(
+				DateRange::create(Date::create('2006-01-01')),
+				DateRange::create(null, Date::create('2006-01-01'))
+			)
+		);
+		$this->assertEquals(1,
+			DateRange::compare(
+				DateRange::create(Date::create('2006-01-01')),
+				DateRange::create(null, Date::create('2007-01-01'))
+			)
+		);
+		$this->assertEquals(-1,
+			DateRange::compare(
+				DateRange::create(Date::create('2006-01-01')),
+				DateRange::create(Date::create('2007-01-01'))
+			)
+		);
+		$this->assertEquals(1,
+			DateRange::compare(
+				DateRange::create(Date::create('2006-01-01')),
+				DateRange::create(null, Date::create('2006-01-01'))
+			)
+		);
+		$this->assertEquals(1,
+			DateRange::compare(
+				DateRange::create(Date::create('2006-01-01')),
+				DateRange::create(null, Date::create('2005-01-01'))
+			)
+		);
+
+		$this->assertEquals(1,
+			DateRange::compare(
+				DateRange::create(Date::create('2006-01-01'), Date::create('2007-01-01')),
+				DateRange::create(null, Date::create('2005-01-01'))
+			)
+		);
+		$this->assertEquals(1,
+			DateRange::compare(
+				DateRange::create(Date::create('2006-01-01'), Date::create('2007-01-01')),
+				DateRange::create(null, Date::create('2006-01-01'))
+			)
+		);
+		$this->assertEquals(1,
+			DateRange::compare(
+				DateRange::create(Date::create('2006-01-01'), Date::create('2007-01-01')),
+				DateRange::create(null, Date::create('2006-06-01'))
+			)
+		);
+		$this->assertEquals(1,
+			DateRange::compare(
+				DateRange::create(Date::create('2006-01-01'), Date::create('2007-01-01')),
+				DateRange::create(null, Date::create('2007-01-01'))
+			)
+		);
+		$this->assertEquals(1,
+			DateRange::compare(
+				DateRange::create(Date::create('2006-01-01'), Date::create('2007-01-01')),
+				DateRange::create(null, Date::create('2008-01-01'))
+			)
+		);
+		$this->assertEquals(1,
+			DateRange::compare(
+				DateRange::create(Date::create('2006-01-01'), Date::create('2007-01-01')),
+				DateRange::create(Date::create('2005-01-01'))
+			)
+		);
+		$this->assertEquals(-1,
+			DateRange::compare(
+				DateRange::create(Date::create('2006-01-01'), Date::create('2007-01-01')),
+				DateRange::create(Date::create('2006-01-01'))
+			)
+		);
+		$this->assertEquals(-1,
+			DateRange::compare(
+				DateRange::create(Date::create('2006-01-01'), Date::create('2007-01-01')),
+				DateRange::create(Date::create('2006-06-01'))
+			)
+		);
+		$this->assertEquals(-1,
+			DateRange::compare(
+				DateRange::create(Date::create('2006-01-01'), Date::create('2007-01-01')),
+				DateRange::create(Date::create('2007-01-01'))
+			)
+		);
+		$this->assertEquals(-1,
+			DateRange::compare(
+				DateRange::create(Date::create('2006-01-01'), Date::create('2007-01-01')),
+				DateRange::create(Date::create('2008-01-01'))
+			)
+		);
+		$this->assertEquals(1,
+			DateRange::compare(
+				DateRange::create(Date::create('2006-01-01'), Date::create('2007-01-01')),
+				DateRange::create(Date::create('2005-01-01'), Date::create('2005-06-01'))
+			)
+		);
+		$this->assertEquals(1,
+			DateRange::compare(
+				DateRange::create(Date::create('2006-01-01'), Date::create('2007-01-01')),
+				DateRange::create(Date::create('2005-01-01'), Date::create('2006-01-01'))
+			)
+		);
+		$this->assertEquals(1,
+			DateRange::compare(
+				DateRange::create(Date::create('2006-01-01'), Date::create('2007-01-01')),
+				DateRange::create(Date::create('2005-01-01'), Date::create('2006-06-01'))
+			)
+		);
+		$this->assertEquals(1,
+			DateRange::compare(
+				DateRange::create(Date::create('2006-01-01'), Date::create('2007-01-01')),
+				DateRange::create(Date::create('2005-01-01'), Date::create('2007-01-01'))
+			)
+		);
+		$this->assertEquals(1,
+			DateRange::compare(
+				DateRange::create(Date::create('2006-01-01'), Date::create('2007-01-01')),
+				DateRange::create(Date::create('2005-01-01'), Date::create('2008-01-01'))
+			)
+		);
+		$this->assertEquals(1,
+			DateRange::compare(
+				DateRange::create(Date::create('2006-01-01'), Date::create('2007-01-01')),
+				DateRange::create(Date::create('2006-01-01'), Date::create('2006-06-01'))
+			)
+		);
+		$this->assertEquals(0,
+			DateRange::compare(
+				DateRange::create(Date::create('2006-01-01'), Date::create('2007-01-01')),
+				DateRange::create(Date::create('2006-01-01'), Date::create('2007-01-01'))
+			)
+		);
+		$this->assertEquals(-1,
+			DateRange::compare(
+				DateRange::create(Date::create('2006-01-01'), Date::create('2007-01-01')),
+				DateRange::create(Date::create('2006-01-01'), Date::create('2008-01-01'))
+			)
+		);
+		$this->assertEquals(-1,
+			DateRange::compare(
+				DateRange::create(Date::create('2006-01-01'), Date::create('2007-01-01')),
+				DateRange::create(Date::create('2006-06-01'), Date::create('2006-07-01'))
+			)
+		);
+		$this->assertEquals(-1,
+			DateRange::compare(
+				DateRange::create(Date::create('2006-01-01'), Date::create('2007-01-01')),
+				DateRange::create(Date::create('2006-06-01'), Date::create('2007-01-01'))
+			)
+		);
+		$this->assertEquals(-1,
+			DateRange::compare(
+				DateRange::create(Date::create('2006-01-01'), Date::create('2007-01-01')),
+				DateRange::create(Date::create('2006-06-01'), Date::create('2008-01-01'))
+			)
+		);
+		$this->assertEquals(-1,
+			DateRange::compare(
+				DateRange::create(Date::create('2006-01-01'), Date::create('2007-01-01')),
+				DateRange::create(Date::create('2007-01-01'), Date::create('2008-01-01'))
+			)
+		);
+		$this->assertEquals(-1,
+			DateRange::compare(
+				DateRange::create(Date::create('2006-01-01'), Date::create('2007-01-01')),
+				DateRange::create(Date::create('2008-01-01'), Date::create('2009-01-01'))
+			)
+		);
+	}
+
+	public function testConstructor()
+	{
+		$dateRange = new DateRange;
+		$this->assertInstanceOf(DateRange::class, $dateRange);
+		$this->assertNull($dateRange->getStart());
+		$this->assertNull($dateRange->getEnd());
+
+		$date = Date::create('2007-01-01');
+		$dateRange = new DateRange($date);
+		$this->assertInstanceOf(DateRange::class, $dateRange);
+		$this->assertInstanceOf(Date::class, $dateRange->getStart());
+		$this->assertEquals($date->toDate(), $dateRange->getStart()->toDate());
+		$this->assertNull($dateRange->getEnd());
+
+		$date = Date::create('2008-01-01');
+		$dateRange = new DateRange(null, $date);
+		$this->assertInstanceOf(DateRange::class, $dateRange);
+		$this->assertNull($dateRange->getStart());
+		$this->assertInstanceOf(Date::class, $dateRange->getEnd());
+		$this->assertEquals($date->toDate(), $dateRange->getEnd()->toDate());
+
+		$start = Date::create('2007-01-01');
+		$end = Date::create('2008-01-01');
+		$dateRange = new DateRange($start, $end);
+		$this->assertInstanceOf(DateRange::class, $dateRange);
+		$this->assertInstanceOf(Date::class, $dateRange->getStart());
+		$this->assertInstanceOf(Date::class, $dateRange->getEnd());
+		$this->assertEquals($start->toDate(), $dateRange->getStart()->toDate());
+		$this->assertEquals($end->toDate(), $dateRange->getEnd()->toDate());
+
+		$start = Date::create('2007-01-01');
+		$end = Date::create('2008-01-01');
+		try {
+			new DateRange($end, $start);
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+	}
+
+	public function testClone()
+	{
+		$dateRange = DateRange::create();
+		$dateRangeClone = clone $dateRange;
+		$this->assertInstanceOf(DateRange::class, $dateRangeClone);
+		$this->assertNull($dateRangeClone->getStart());
+		$this->assertNull($dateRangeClone->getEnd());
+
+		$date = Date::create('2007-01-01');
+		$dateRange = DateRange::create($date);
+		$dateRangeClone = clone $dateRange;
+		$this->assertInstanceOf(DateRange::class, $dateRangeClone);
+		$this->assertInstanceOf(Date::class, $dateRangeClone->getStart());
+		$this->assertEquals($date->toDate(), $dateRangeClone->getStart()->toDate());
+		$this->assertNull($dateRangeClone->getEnd());
+		$dateRange->dropStart();
+		$this->assertInstanceOf(Date::class, $dateRangeClone->getStart());
+
+		$date = Date::create('2008-01-01');
+		$dateRange = DateRange::create(null, $date);
+		$dateRangeClone = clone $dateRange;
+		$this->assertInstanceOf(DateRange::class, $dateRangeClone);
+		$this->assertNull($dateRangeClone->getStart());
+		$this->assertInstanceOf(Date::class, $dateRangeClone->getEnd());
+		$this->assertEquals($date->toDate(), $dateRangeClone->getEnd()->toDate());
+		$dateRange->dropEnd();
+		$this->assertInstanceOf(Date::class, $dateRangeClone->getEnd());
+
+		$start = Date::create('2007-01-01');
+		$end = Date::create('2008-01-01');
+		$dateRange = DateRange::create($start, $end);
+		$dateRangeClone = clone $dateRange;
+		$this->assertInstanceOf(DateRange::class, $dateRangeClone);
+		$this->assertInstanceOf(Date::class, $dateRangeClone->getStart());
+		$this->assertInstanceOf(Date::class, $dateRangeClone->getEnd());
+		$this->assertEquals($start->toDate(), $dateRangeClone->getStart()->toDate());
+		$this->assertEquals($end->toDate(), $dateRangeClone->getEnd()->toDate());
+		$dateRange->dropStart()->dropEnd();
+		$this->assertInstanceOf(Date::class, $dateRangeClone->getStart());
+		$this->assertInstanceOf(Date::class, $dateRangeClone->getEnd());
+	}
+
+	public function testSetStart()
+	{
+		$dateRange = DateRange::create();
+		$start = Date::create('2007-01-01');
+		$end = Date::create('2008-01-01');
+
+		$dateRange->setStart($end);
+		$this->assertInstanceOf(Date::class, $dateRange->getStart());
+		$this->assertEquals($end->toDate(), $dateRange->getStart()->toDate());
+		$dateRange->setStart($start);
+		$this->assertInstanceOf(Date::class, $dateRange->getStart());
+		$this->assertEquals($start->toDate(), $dateRange->getStart()->toDate());
+		$dateRange->setEnd($start);
+		try {
+			$dateRange->setStart($end);
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+	}
+
+	public function testSafeSetStart()
+	{
+		$dateRange = DateRange::create();
+		$start = Date::create('2007-01-01');
+		$end = Date::create('2008-01-01');
+
+		$dateRange->safeSetStart($start);
+		$this->assertInstanceOf(Date::class, $dateRange->getStart());
+		$this->assertEquals($start->toDate(), $dateRange->getStart()->toDate());
+
+		$dateRange = DateRange::create(null, $start);
+		$dateRange->safeSetStart($end);
+		$this->assertInstanceOf(Date::class, $dateRange->getStart());
+		$this->assertInstanceOf(Date::class, $dateRange->getEnd());
+		$this->assertEquals($dateRange->getEnd()->toDate(), $dateRange->getStart()->toDate());
+		$this->assertEquals($start->toDate(), $dateRange->getStart()->toDate());
+
+		$dateRange = DateRange::create(null, $end);
+		$dateRange->safeSetStart($start);
+		$this->assertInstanceOf(Date::class, $dateRange->getStart());
+		$this->assertEquals($start->toDate(), $dateRange->getStart()->toDate());
+	}
+
+	public function testSafeSetEnd()
+	{
+		$dateRange = DateRange::create();
+		$start = Date::create('2007-01-01');
+		$end = Date::create('2008-01-01');
+
+		$dateRange->safeSetEnd($end);
+		$this->assertInstanceOf(Date::class, $dateRange->getEnd());
+		$this->assertEquals($end->toDate(), $dateRange->getEnd()->toDate());
+
+		$dateRange = DateRange::create($end);
+		$dateRange->safeSetEnd($start);
+		$this->assertInstanceOf(Date::class, $dateRange->getStart());
+		$this->assertInstanceOf(Date::class, $dateRange->getEnd());
+		$this->assertEquals($dateRange->getEnd()->toDate(), $dateRange->getStart()->toDate());
+		$this->assertEquals($end->toDate(), $dateRange->getEnd()->toDate());
+
+		$dateRange = DateRange::create($start);
+		$dateRange->safeSetEnd($end);
+		$this->assertInstanceOf(Date::class, $dateRange->getEnd());
+		$this->assertEquals($end->toDate(), $dateRange->getEnd()->toDate());
+	}
+
+	public function testSetEnd()
+	{
+		$dateRange = DateRange::create();
+		$start = Date::create('2007-01-01');
+		$end = Date::create('2008-01-01');
+
+		$dateRange->setEnd($start);
+		$this->assertInstanceOf(Date::class, $dateRange->getEnd());
+		$this->assertEquals($start->toDate(), $dateRange->getEnd()->toDate());
+		$dateRange->setEnd($end);
+		$this->assertInstanceOf(Date::class, $dateRange->getEnd());
+		$this->assertEquals($end->toDate(), $dateRange->getEnd()->toDate());
+		$dateRange->setStart($end);
+		try {
+			$dateRange->setEnd($start);
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+	}
+
+	public function testLazySet()
+	{
+		$dateRange = DateRange::create()->lazySet();
+		$this->assertNull($dateRange->getStart());
+		$this->assertNull($dateRange->getEnd());
+
+		$date = Date::create('2007-01-01');
+		$dateRange = DateRange::create()->lazySet($date);
+		$this->assertInstanceOf(Date::class, $dateRange->getStart());
+		$this->assertEquals($date->toDate(), $dateRange->getStart()->toDate());
+		$this->assertNull($dateRange->getEnd());
+		$dateRange = DateRange::create()->lazySet(null, $date);
+		$this->assertInstanceOf(Date::class, $dateRange->getEnd());
+		$this->assertEquals($date->toDate(), $dateRange->getEnd()->toDate());
+		$this->assertNull($dateRange->getStart());
+
+		$start = Date::create('2007-01-01');
+		$end = Date::create('2008-01-01');
+		$dateRange = DateRange::create()->lazySet($start, $end);
+		$this->assertInstanceOf(Date::class, $dateRange->getStart());
+		$this->assertInstanceOf(Date::class, $dateRange->getEnd());
+		$this->assertEquals($start->toDate(), $dateRange->getStart()->toDate());
+		$this->assertEquals($end->toDate(), $dateRange->getEnd()->toDate());
+		$dateRange = DateRange::create()->lazySet($end, $start);
+		$this->assertInstanceOf(Date::class, $dateRange->getStart());
+		$this->assertInstanceOf(Date::class, $dateRange->getEnd());
+		$this->assertEquals($start->toDate(), $dateRange->getStart()->toDate());
+		$this->assertEquals($end->toDate(), $dateRange->getEnd()->toDate());
+	}
+
+	public function testDropStart()
+	{
+		$dateRange = DateRange::create();
+		$start = Date::create('2007-01-01');
+		$dateRange->dropStart();
+
+		$dateRange->setStart($start);
+		$dateRange->dropStart();
+		$this->assertNull($dateRange->getStart());
+		$this->assertNull($dateRange->getStartStamp());
+	}
+
+	public function testDropEnd()
+	{
+		$dateRange = DateRange::create();
+		$end = Date::create('2008-01-01');
+		$dateRange->dropEnd();
+
+		$dateRange->setEnd($end);
+		$dateRange->dropEnd();
+		$this->assertNull($dateRange->getEnd());
+		$this->assertNull($dateRange->getEndStamp());
+	}
+
+	public function testIsEmpty()
+	{
+		$this->assertTrue(DateRange::create()->isEmpty());
+		$this->assertFalse(DateRange::create(Date::create('2007-01-01'), null)->isEmpty());
+		$this->assertFalse(DateRange::create(null, Date::create('2008-01-01'))->isEmpty());
+		$this->assertFalse(
+			DateRange::create(Date::create('2007-01-01'), Date::create('2008-01-01'))->isEmpty()
+		);
+	}
+
+	public function testGetStart()
+	{
+		$dateRange = DateRange::create();
+		$this->assertNull($dateRange->getStart());
+
+		$date = Date::create('2007-01-01');
+		$dateRange = DateRange::create($date);
+		$this->assertInstanceOf(Date::class, $dateRange->getStart());
+		$this->assertEquals($date->toDate(), $dateRange->getStart()->toDate());
+		$dateRange->dropStart();
+		$this->assertNull($dateRange->getStart());
+	}
+
+	public function testGetEnd()
+	{
+		$dateRange = DateRange::create();
+		$this->assertNull($dateRange->getEnd());
+
+		$date = Date::create('2007-12-31');
+		$dateRange = DateRange::create(null, $date);
+		$this->assertInstanceOf(Date::class, $dateRange->getEnd());
+		$this->assertEquals($date->toDate(), $dateRange->getEnd()->toDate());
+		$dateRange->dropEnd();
+		$this->assertNull($dateRange->getEnd());
+	}
+
+	public function testToDateString()
+	{
+		$start = Date::create('2007-01-01');
+		$end = Date::create('2007-12-31');
+		$methodParams = [
+			'internalDelimiter' => '-',
+			'dateDelimiter' => ' - ',
+		];
+
+		$dateRangeReflection = new \ReflectionClass(DateRange::class);
+		$toDateStringMethod = $dateRangeReflection->getMethod('toDateString');
+		$this->assertCount($toDateStringMethod->getNumberOfParameters(), $methodParams);
+		foreach ($toDateStringMethod->getParameters() as $param) {
+			$this->assertArrayHasKey($param->getName(), $methodParams);
+			$this->assertEquals($methodParams[$param->getName()], $param->getDefaultValue());
+		}
+
+		$this->assertNull(DateRange::create()->toDateString());
+		$this->assertEquals(
+			$start->toDate($methodParams['internalDelimiter']) . $methodParams['dateDelimiter'] . $end->toDate($methodParams['internalDelimiter']),
+			DateRange::create($start, $end)->toDateString()
+		);
+		$this->assertEquals($start->toDate($methodParams['internalDelimiter']), DateRange::create($start)->toDateString());
+		$this->assertEquals($end->toDate($methodParams['internalDelimiter']), DateRange::create(null, $end)->toDateString());
+	}
+
+	public function testToString()
+	{
+		$start = Date::create('2007-01-01');
+		$end = Date::create('2007-12-31');
+		$methodParams = [
+			'delimiter' => ' - ',
+		];
+
+		$dateRangeReflection = new \ReflectionClass(DateRange::class);
+		$toDateStringMethod = $dateRangeReflection->getMethod('toString');
+		$this->assertCount($toDateStringMethod->getNumberOfParameters(), $methodParams);
+		foreach ($toDateStringMethod->getParameters() as $param) {
+			$this->assertArrayHasKey($param->getName(), $methodParams);
+			$this->assertEquals($methodParams[$param->getName()], $param->getDefaultValue());
+		}
+
+		$this->assertNull(DateRange::create()->toString());
+		$this->assertEquals(
+			$start->toDate() . $methodParams['delimiter'] . $end->toDate(),
+			DateRange::create($start, $end)->toDateString()
+		);
+		$this->assertEquals($start->toDate(), DateRange::create($start)->toDateString());
+		$this->assertEquals($end->toDate(), DateRange::create(null, $end)->toDateString());
+	}
+
+	public function testOverlaps()
+	{
+		$dataRange = DateRange::create()->lazySet(Date::create('2007-01-01'), Date::create('2007-12-31'));
+
+		$this->assertTrue($dataRange->overlaps(DateRange::create()));
+
+		$this->assertTrue($dataRange->overlaps(DateRange::create()->setStart(Date::create('2006-12-31'))));
+		$this->assertFalse(
+			$dataRange
+				->overlaps(
+					DateRange::create()
+						->setStart(Date::create('2006-12-01'))
+						->setEnd(Date::create('2006-12-31'))
+				)
+		);
+		$this->assertFalse($dataRange->overlaps(DateRange::create()->setEnd(Date::create('2006-12-31'))));
+
+		$this->assertTrue(
+			$dataRange
+				->overlaps(
+					DateRange::create()
+						->setStart(Date::create('2006-01-01'))
+						->setEnd(Date::create('2007-01-01'))
+				)
+		);
+		$this->assertTrue(
+			$dataRange
+				->overlaps(
+					DateRange::create()
+						->setStart(Date::create('2007-12-31'))
+						->setEnd(Date::create('2008-12-31'))
+				)
+		);
+		$this->assertTrue(
+			$dataRange
+				->overlaps(
+					DateRange::create()
+						->setStart(Date::create('2007-01-01'))
+						->setEnd(Date::create('2007-12-31'))
+				)
+		);
+		$this->assertTrue($dataRange->overlaps(DateRange::create()->setStart(Date::create('2007-12-31'))));
+		$this->assertTrue($dataRange->overlaps(DateRange::create()->setEnd(Date::create('2007-01-01'))));
+		$this->assertTrue(
+			$dataRange
+				->overlaps(
+					DateRange::create()
+						->setStart(Date::create('2007-02-01'))
+						->setEnd(Date::create('2007-03-01'))
+				)
+		);
+		$this->assertTrue($dataRange->overlaps(DateRange::create()->setStart(Date::create('2007-06-12'))));
+		$this->assertTrue($dataRange->overlaps(DateRange::create()->setEnd(Date::create('2007-06-01'))));
+
+		$this->assertFalse($dataRange->overlaps(DateRange::create()->setStart(Date::create('2008-01-01'))));
+		$this->assertFalse(
+			$dataRange
+				->overlaps(
+					DateRange::create()
+						->setStart(Date::create('2008-01-01'))
+						->setEnd(Date::create('2008-12-31'))
+				)
+		);
+		$this->assertTrue(
+			$dataRange
+				->overlaps(
+					DateRange::create()
+						->setEnd(Date::create('2006-12-31'))
+						->setEnd(Date::create('2008-01-01'))
+				)
+		);
+		$this->assertTrue(
+			$dataRange->overlaps(
+				DateRange::create()->lazySet(Date::create('2007-05-14'), Date::create('2008-03-29'))
+			)
+		);
+		$this->assertTrue(
+			$dataRange->overlaps(
+				DateRange::create()->lazySet(Date::create('2006-05-14'), Date::create('2007-03-29'))
+			)
+		);
+
+		$this->assertTrue(DateRange::create()->overlaps(DateRange::create()));
+		$this->assertTrue(
+			DateRange::create()
+				->overlaps(
+					DateRange::create()->lazySet(Date::create('2007-03-28'), Date::create('2008-03-27'))
+				)
+		);
+	}
+
+	public function testContains()
+	{
+		$this->assertTrue(DateRange::create()->contains(Date::create('2007-06-01')));
+
+		$dataRange = DateRange::create()->lazySet(Date::create('2007-01-01'), Date::create('2007-12-31'));
+		$this->assertTrue($dataRange->contains(Date::create('2007-06-01')));
+		$this->assertTrue($dataRange->contains(Date::create('2007-01-01')));
+		$this->assertTrue($dataRange->contains(Date::create('2007-12-31')));
+		$this->assertFalse($dataRange->contains(Date::create('2006-06-01')));
+		$this->assertFalse($dataRange->contains(Date::create('2008-06-01')));
+
+		$dataRange = DateRange::create()->setStart(Date::create('2007-01-01'));
+		$this->assertTrue($dataRange->contains(Date::create('2007-06-01')));
+		$this->assertTrue($dataRange->contains(Date::create('2007-01-01')));
+		$this->assertTrue($dataRange->contains(Date::create('2007-12-31')));
+		$this->assertFalse($dataRange->contains(Date::create('2006-06-01')));
+
+		$dataRange = DateRange::create()->setEnd(Date::create('2007-12-31'));
+		$this->assertTrue($dataRange->contains(Date::create('2007-06-01')));
+		$this->assertTrue($dataRange->contains(Date::create('2007-12-31')));
+		$this->assertFalse($dataRange->contains(Date::create('2008-06-01')));
+	}
+
 	public function testSplit()
 	{
 		$start = new Date('2007-03-26');
@@ -21,39 +817,1075 @@ public function testSplit()
 
 		$dates = $range->split();
 
-		$this->assertEquals(count($dates), 21);
+		$this->assertCount(21, $dates);
 
 		$this->assertEquals(reset($dates), $start);
 		$this->assertEquals(end($dates), $end);
+
+		try {
+			DateRange::create()->split();
+			$this->fail('expected WrongArgumentException exception');
+		} catch (\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+		try {
+			DateRange::create()->setStart(Date::create('2007-01-01'))->split();
+			$this->fail('expected WrongArgumentException exception');
+		} catch (\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+		try {
+			DateRange::create()->setEnd(Date::create('2006-12-31'))->split();
+			$this->fail('expected WrongArgumentException exception');
+		} catch (\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+
+		$start = $end = Date::create('2006-01-01');
+		$ranges = DateRange::create($start, $end)->split();
+		$this->assertCount(1, $ranges);
+		$rangeDate = current($ranges);
+		$this->assertEquals($rangeDate, $start);
+		$this->assertEquals($rangeDate, $end);
 	}
 
-	public function testOverlaps()
+	public function testIsNeighbour()
 	{
-		$this->assertTrue(
-			DateRange::create()->lazySet(
-				Date::create('2007-03-28'),
-				Date::create('2008-03-27')
-			)->
-			overlaps(
-				DateRange::create()->lazySet(
-					Date::create('2007-05-14'),
-					Date::create('2008-03-29')
-				)
-			)
-		);
+		$dateRangeEmpty = DateRange::create();
+		$dateRange = DateRange::create(Date::create('2007-01-01'), Date::create('2007-12-31'));
+
+		try {
+			$dateRangeEmpty->isNeighbour($dateRangeEmpty);
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+
+		try {
+			$dateRangeEmpty->isNeighbour($dateRange);
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+		try {
+			$dateRangeEmpty->isNeighbour(DateRange::create()->setStart(Date::create('2007-01-01')));
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+		try {
+			$dateRangeEmpty->isNeighbour(DateRange::create()->setEnd(Date::create('2007-12-31')));
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+
+		try {
+			$dateRange->isNeighbour($dateRangeEmpty);
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+		try {
+			$dateRange->isNeighbour(DateRange::create()->setStart(Date::create('2007-01-01')));
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+		try {
+			$dateRange->isNeighbour(DateRange::create()->setEnd(Date::create('2007-12-31')));
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+
+		try {
+			DateRange::create()
+				->setStart(Date::create('2007-01-01'))
+				->isNeighbour($dateRange);
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+		try {
+			DateRange::create()
+				->setStart(Date::create('2007-01-01'))
+				->isNeighbour($dateRangeEmpty);
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+		try {
+			DateRange::create()
+				->setStart(Date::create('2007-01-01'))
+				->isNeighbour(DateRange::create()->setStart(Date::create('2007-01-01')));
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+		try {
+			DateRange::create()
+				->setStart(Date::create('2007-01-01'))
+				->isNeighbour(DateRange::create()->setEnd(Date::create('2007-12-31')));
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+
+		try {
+			DateRange::create()
+				->setEnd(Date::create('2007-12-31'))
+				->isNeighbour($dateRange);
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+		try {
+			DateRange::create()
+				->setEnd(Date::create('2007-12-31'))
+				->isNeighbour($dateRangeEmpty);
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+		try {
+			DateRange::create()
+				->setEnd(Date::create('2007-12-31'))
+				->isNeighbour(DateRange::create()->setStart(Date::create('2007-01-01')));
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+		try {
+			DateRange::create()
+				->setEnd(Date::create('2007-12-31'))
+				->isNeighbour(DateRange::create()->setEnd(Date::create('2007-12-31')));
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
 
 		$this->assertFalse(
-			DateRange::create()->lazySet(
-				Date::create('2007-03-28'),
-				Date::create('2008-03-27')
-			)->
-			overlaps(
-				DateRange::create()->lazySet(
-					Date::create('2005-05-14'),
-					Date::create('2006-03-29')
-				)
-			)
+			$dateRange
+				->isNeighbour(DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-01')))
+		);
+		$this->assertFalse(
+			$dateRange
+				->isNeighbour(DateRange::create(Date::create('2008-02-01'), Date::create('2008-12-31')))
+		);
+		$this->assertTrue(
+			$dateRange
+				->isNeighbour(DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31')))
+		);
+		$this->assertTrue(
+			$dateRange
+				->isNeighbour(DateRange::create(Date::create('2008-01-01'), Date::create('2008-12-31')))
+		);
+		$this->assertTrue(
+			$dateRange
+				->isNeighbour(DateRange::create(Date::create('2007-12-31'), Date::create('2008-12-31')))
 		);
+		$this->assertTrue(
+			$dateRange
+				->isNeighbour(DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31')))
+		);
+		$this->assertTrue(
+			$dateRange
+				->isNeighbour(DateRange::create(Date::create('2006-01-01'), Date::create('2007-01-01')))
+		);
+		$this->assertTrue(
+			$dateRange
+				->isNeighbour(DateRange::create(Date::create('2006-01-01'), Date::create('2007-06-01')))
+		);
+		$this->assertTrue(
+			$dateRange
+				->isNeighbour(DateRange::create(Date::create('2007-06-01'), Date::create('2008-06-01')))
+		);
+		$this->assertTrue(
+			$dateRange
+				->isNeighbour(DateRange::create(Date::create('2007-06-01'), Date::create('2007-07-01')))
+		);
+	}
+
+	public function testIsOpen()
+	{
+		$this->assertTrue(DateRange::create()->isOpen());
+		$this->assertTrue(DateRange::create(Date::create('2007-06-01'))->isOpen());
+		$this->assertTrue(DateRange::create()->setEnd(Date::create('2007-06-01'))->isOpen());
+		$this->assertFalse(DateRange::create(Date::create('2007-06-01'), Date::create('2007-06-01'))->isOpen());
+	}
+
+	public function testEnlarge()
+	{
+		$dateRange = DateRange::create()->enlarge(DateRange::create());
+		$this->assertNull($dateRange->getStart());
+		$this->assertNull($dateRange->getEnd());
+
+		$dateRange = DateRange::create()->enlarge(DateRange::create(Date::create('2007-01-01')));
+		$this->assertNull($dateRange->getStart());
+		$this->assertNull($dateRange->getEnd());
+		$dateRange = DateRange::create()->enlarge(DateRange::create(null, Date::create('2007-01-01')));
+		$this->assertNull($dateRange->getStart());
+		$this->assertNull($dateRange->getEnd());
+		$dateRange = DateRange::create()->enlarge(DateRange::create(Date::create('2006-01-01'), Date::create('2007-01-01')));
+		$this->assertNull($dateRange->getStart());
+		$this->assertNull($dateRange->getEnd());
+
+		$dateRange = DateRange::create(Date::create('2007-01-01'))->enlarge(DateRange::create());
+		$this->assertNull($dateRange->getStart());
+		$this->assertNull($dateRange->getEnd());
+		$dateRange = DateRange::create(Date::create('2007-01-01'))
+			->enlarge(DateRange::create(Date::create('2006-01-01')));
+		$this->assertEquals($dateRange->getStart()->toDate(), Date::create('2006-01-01')->toDate());
+		$this->assertNull($dateRange->getEnd());
+		$dateRange = DateRange::create(Date::create('2007-01-01'))
+			->enlarge(DateRange::create(Date::create('2007-01-01')));
+		$this->assertEquals($dateRange->getStart()->toDate(), Date::create('2007-01-01')->toDate());
+		$this->assertNull($dateRange->getEnd());
+		$dateRange = DateRange::create(Date::create('2007-01-01'))
+			->enlarge(DateRange::create(Date::create('2008-01-01')));
+		$this->assertEquals($dateRange->getStart()->toDate(), Date::create('2007-01-01')->toDate());
+		$this->assertNull($dateRange->getEnd());
+		$dateRange = DateRange::create(Date::create('2007-01-01'))
+			->enlarge(DateRange::create(null, Date::create('2006-01-01')));
+		$this->assertNull($dateRange->getStart());
+		$this->assertNull($dateRange->getEnd());
+		$dateRange = DateRange::create(Date::create('2007-01-01'))
+			->enlarge(DateRange::create(null, Date::create('2007-01-01')));
+		$this->assertNull($dateRange->getStart());
+		$this->assertNull($dateRange->getEnd());
+		$dateRange = DateRange::create(Date::create('2007-01-01'))
+			->enlarge(DateRange::create(null, Date::create('2008-01-01')));
+		$this->assertNull($dateRange->getStart());
+		$this->assertNull($dateRange->getEnd());
+		$dateRange = DateRange::create(Date::create('2007-01-01'))
+			->enlarge(DateRange::create(Date::create('2006-01-01'), Date::create('2006-06-01')));
+		$this->assertEquals($dateRange->getStart()->toDate(), Date::create('2006-01-01')->toDate());
+		$this->assertNull($dateRange->getEnd());
+		$dateRange = DateRange::create(Date::create('2007-01-01'))
+			->enlarge(DateRange::create(Date::create('2006-01-01'), Date::create('2007-01-01')));
+		$this->assertEquals($dateRange->getStart()->toDate(), Date::create('2006-01-01')->toDate());
+		$this->assertNull($dateRange->getEnd());
+		$dateRange = DateRange::create(Date::create('2007-01-01'))
+			->enlarge(DateRange::create(Date::create('2006-01-01'), Date::create('2008-01-01')));
+		$this->assertEquals($dateRange->getStart()->toDate(), Date::create('2006-01-01')->toDate());
+		$this->assertNull($dateRange->getEnd());
+		$dateRange = DateRange::create(Date::create('2007-01-01'))
+			->enlarge(DateRange::create(Date::create('2007-01-01'), Date::create('2008-01-01')));
+		$this->assertEquals($dateRange->getStart()->toDate(), Date::create('2007-01-01')->toDate());
+		$this->assertNull($dateRange->getEnd());
+		$dateRange = DateRange::create(Date::create('2007-01-01'))
+			->enlarge(DateRange::create(Date::create('2008-01-01'), Date::create('2008-06-01')));
+		$this->assertEquals($dateRange->getStart()->toDate(), Date::create('2007-01-01')->toDate());
+		$this->assertNull($dateRange->getEnd());
+
+		$dateRange = DateRange::create(null, Date::create('2007-01-01'))->enlarge(DateRange::create());
+		$this->assertNull($dateRange->getStart());
+		$this->assertNull($dateRange->getEnd());
+		$dateRange = DateRange::create(null, Date::create('2007-01-01'))
+			->enlarge(DateRange::create(Date::create('2006-01-01')));
+		$this->assertNull($dateRange->getStart());
+		$this->assertNull($dateRange->getEnd());
+		$dateRange = DateRange::create(null, Date::create('2007-01-01'))
+			->enlarge(DateRange::create(Date::create('2007-01-01')));
+		$this->assertNull($dateRange->getStart());
+		$this->assertNull($dateRange->getEnd());
+		$dateRange = DateRange::create(null, Date::create('2007-01-01'))
+			->enlarge(DateRange::create(Date::create('2008-01-01')));
+		$this->assertNull($dateRange->getStart());
+		$this->assertNull($dateRange->getEnd());
+		$dateRange = DateRange::create(null, Date::create('2007-01-01'))
+			->enlarge(DateRange::create(null, Date::create('2006-01-01')));
+		$this->assertNull($dateRange->getStart());
+		$this->assertEquals($dateRange->getEnd()->toDate(), Date::create('2007-01-01')->toDate());
+		$dateRange = DateRange::create(null, Date::create('2007-01-01'))
+			->enlarge(DateRange::create(null, Date::create('2007-01-01')));
+		$this->assertNull($dateRange->getStart());
+		$this->assertEquals($dateRange->getEnd()->toDate(), Date::create('2007-01-01')->toDate());
+		$dateRange = DateRange::create(null, Date::create('2007-01-01'))
+			->enlarge(DateRange::create(null, Date::create('2008-01-01')));
+		$this->assertNull($dateRange->getStart());
+		$this->assertEquals($dateRange->getEnd()->toDate(), Date::create('2008-01-01')->toDate());
+		$dateRange = DateRange::create(null, Date::create('2007-01-01'))
+			->enlarge(DateRange::create(Date::create('2006-01-01'), Date::create('2006-06-01')));
+		$this->assertNull($dateRange->getStart());
+		$this->assertEquals($dateRange->getEnd()->toDate(), Date::create('2007-01-01')->toDate());
+		$dateRange = DateRange::create(null, Date::create('2007-01-01'))
+			->enlarge(DateRange::create(Date::create('2006-01-01'), Date::create('2007-01-01')));
+		$this->assertNull($dateRange->getStart());
+		$this->assertEquals($dateRange->getEnd()->toDate(), Date::create('2007-01-01')->toDate());
+		$dateRange = DateRange::create(null, Date::create('2007-01-01'))
+			->enlarge(DateRange::create(Date::create('2006-01-01'), Date::create('2008-01-01')));
+		$this->assertNull($dateRange->getStart());
+		$this->assertEquals($dateRange->getEnd()->toDate(), Date::create('2008-01-01')->toDate());
+		$dateRange = DateRange::create(null, Date::create('2007-01-01'))
+			->enlarge(DateRange::create(Date::create('2007-01-01'), Date::create('2008-01-01')));
+		$this->assertNull($dateRange->getStart());
+		$this->assertEquals($dateRange->getEnd()->toDate(), Date::create('2008-01-01')->toDate());
+		$dateRange = DateRange::create(null, Date::create('2007-01-01'))
+			->enlarge(DateRange::create(Date::create('2008-01-01'), Date::create('2008-06-01')));
+		$this->assertNull($dateRange->getStart());
+		$this->assertEquals($dateRange->getEnd()->toDate(), Date::create('2008-06-01')->toDate());
+
+		$dateRange = DateRange::create(Date::create('2007-01-01'), Date::create('2007-12-31'))
+			->enlarge(DateRange::create());
+		$this->assertNull($dateRange->getStart());
+		$this->assertNull($dateRange->getEnd());
+		$dateRange = DateRange::create(Date::create('2007-01-01'), Date::create('2007-12-31'))
+			->enlarge(DateRange::create(Date::create('2006-01-01')));
+		$this->assertEquals($dateRange->getStart()->toDate(), Date::create('2006-01-01')->toDate());
+		$this->assertNull($dateRange->getEnd());
+		$dateRange = DateRange::create(Date::create('2007-01-01'), Date::create('2007-12-31'))
+			->enlarge(DateRange::create(Date::create('2007-01-01')));
+		$this->assertEquals($dateRange->getStart()->toDate(), Date::create('2007-01-01')->toDate());
+		$this->assertNull($dateRange->getEnd());
+		$dateRange = DateRange::create(Date::create('2007-01-01'), Date::create('2007-12-31'))
+			->enlarge(DateRange::create(Date::create('2007-06-01')));
+		$this->assertEquals($dateRange->getStart()->toDate(), Date::create('2007-01-01')->toDate());
+		$this->assertNull($dateRange->getEnd());
+		$dateRange = DateRange::create(Date::create('2007-01-01'), Date::create('2007-12-31'))
+			->enlarge(DateRange::create(Date::create('2007-12-31')));
+		$this->assertEquals($dateRange->getStart()->toDate(), Date::create('2007-01-01')->toDate());
+		$this->assertNull($dateRange->getEnd());
+		$dateRange = DateRange::create(Date::create('2007-01-01'), Date::create('2007-12-31'))
+			->enlarge(DateRange::create(Date::create('2008-01-01')));
+		$this->assertEquals($dateRange->getStart()->toDate(), Date::create('2007-01-01')->toDate());
+		$this->assertNull($dateRange->getEnd());
+		$dateRange = DateRange::create(Date::create('2007-01-01'), Date::create('2007-12-31'))
+			->enlarge(DateRange::create(null, Date::create('2006-01-01')));
+		$this->assertNull($dateRange->getStart());
+		$this->assertEquals($dateRange->getEnd()->toDate(), Date::create('2007-12-31')->toDate());
+		$dateRange = DateRange::create(Date::create('2007-01-01'), Date::create('2007-12-31'))
+			->enlarge(DateRange::create(null, Date::create('2007-01-01')));
+		$this->assertNull($dateRange->getStart());
+		$this->assertEquals($dateRange->getEnd()->toDate(), Date::create('2007-12-31')->toDate());
+		$dateRange = DateRange::create(Date::create('2007-01-01'), Date::create('2007-12-31'))
+			->enlarge(DateRange::create(null, Date::create('2007-06-01')));
+		$this->assertNull($dateRange->getStart());
+		$this->assertEquals($dateRange->getEnd()->toDate(), Date::create('2007-12-31')->toDate());
+		$dateRange = DateRange::create(Date::create('2007-01-01'), Date::create('2007-12-31'))
+			->enlarge(DateRange::create(null, Date::create('2007-12-31')));
+		$this->assertNull($dateRange->getStart());
+		$this->assertEquals($dateRange->getEnd()->toDate(), Date::create('2007-12-31')->toDate());
+		$dateRange = DateRange::create(Date::create('2007-01-01'), Date::create('2007-12-31'))
+			->enlarge(DateRange::create(null, Date::create('2008-12-31')));
+		$this->assertNull($dateRange->getStart());
+		$this->assertEquals($dateRange->getEnd()->toDate(), Date::create('2008-12-31')->toDate());
+		$dateRange = DateRange::create(Date::create('2007-01-01'), Date::create('2007-12-31'))
+			->enlarge(DateRange::create(Date::create('2006-01-01'), Date::create('2006-06-01')));
+		$this->assertEquals($dateRange->getStart()->toDate(), Date::create('2006-01-01')->toDate());
+		$this->assertEquals($dateRange->getEnd()->toDate(), Date::create('2007-12-31')->toDate());
+		$dateRange = DateRange::create(Date::create('2007-01-01'), Date::create('2007-12-31'))
+			->enlarge(DateRange::create(Date::create('2006-01-01'), Date::create('2007-01-01')));
+		$this->assertEquals($dateRange->getStart()->toDate(), Date::create('2006-01-01')->toDate());
+		$this->assertEquals($dateRange->getEnd()->toDate(), Date::create('2007-12-31')->toDate());
+		$dateRange = DateRange::create(Date::create('2007-01-01'), Date::create('2007-12-31'))
+			->enlarge(DateRange::create(Date::create('2006-01-01'), Date::create('2007-06-01')));
+		$this->assertEquals($dateRange->getStart()->toDate(), Date::create('2006-01-01')->toDate());
+		$this->assertEquals($dateRange->getEnd()->toDate(), Date::create('2007-12-31')->toDate());
+		$dateRange = DateRange::create(Date::create('2007-01-01'), Date::create('2007-12-31'))
+			->enlarge(DateRange::create(Date::create('2007-01-01'), Date::create('2007-06-01')));
+		$this->assertEquals($dateRange->getStart()->toDate(), Date::create('2007-01-01')->toDate());
+		$this->assertEquals($dateRange->getEnd()->toDate(), Date::create('2007-12-31')->toDate());
+		$dateRange = DateRange::create(Date::create('2007-01-01'), Date::create('2007-12-31'))
+			->enlarge(DateRange::create(Date::create('2007-01-01'), Date::create('2007-12-31')));
+		$this->assertEquals($dateRange->getStart()->toDate(), Date::create('2007-01-01')->toDate());
+		$this->assertEquals($dateRange->getEnd()->toDate(), Date::create('2007-12-31')->toDate());
+		$dateRange = DateRange::create(Date::create('2007-01-01'), Date::create('2007-12-31'))
+			->enlarge(DateRange::create(Date::create('2007-02-01'), Date::create('2007-10-01')));
+		$this->assertEquals($dateRange->getStart()->toDate(), Date::create('2007-01-01')->toDate());
+		$this->assertEquals($dateRange->getEnd()->toDate(), Date::create('2007-12-31')->toDate());
+		$dateRange = DateRange::create(Date::create('2007-01-01'), Date::create('2007-12-31'))
+			->enlarge(DateRange::create(Date::create('2007-02-01'), Date::create('2007-12-31')));
+		$this->assertEquals($dateRange->getStart()->toDate(), Date::create('2007-01-01')->toDate());
+		$this->assertEquals($dateRange->getEnd()->toDate(), Date::create('2007-12-31')->toDate());
+		$dateRange = DateRange::create(Date::create('2007-01-01'), Date::create('2007-12-31'))
+			->enlarge(DateRange::create(Date::create('2007-02-01'), Date::create('2008-12-31')));
+		$this->assertEquals($dateRange->getStart()->toDate(), Date::create('2007-01-01')->toDate());
+		$this->assertEquals($dateRange->getEnd()->toDate(), Date::create('2008-12-31')->toDate());
+		$dateRange = DateRange::create(Date::create('2007-01-01'), Date::create('2007-12-31'))
+			->enlarge(DateRange::create(Date::create('2007-12-31'), Date::create('2008-12-31')));
+		$this->assertEquals($dateRange->getStart()->toDate(), Date::create('2007-01-01')->toDate());
+		$this->assertEquals($dateRange->getEnd()->toDate(), Date::create('2008-12-31')->toDate());
+		$dateRange = DateRange::create(Date::create('2007-01-01'), Date::create('2007-12-31'))
+			->enlarge(DateRange::create(Date::create('2008-06-01'), Date::create('2008-12-31')));
+		$this->assertEquals($dateRange->getStart()->toDate(), Date::create('2007-01-01')->toDate());
+		$this->assertEquals($dateRange->getEnd()->toDate(), Date::create('2008-12-31')->toDate());
+	}
+
+	public function testClip()
+	{
+		$clip = DateRange::create()->clip(DateRange::create());
+		$this->assertInstanceOf(DateRange::class, $clip);
+		$this->assertNull($clip->getStart());
+		$this->assertNull($clip->getEnd());
+
+		$clip = DateRange::create(null, Date::create('2006-01-01'))
+			->clip(DateRange::create());
+		$this->assertNull($clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(null, Date::create('2006-01-01'))
+			->clip(DateRange::create(null, Date::create('2005-01-01')));
+		$this->assertNull($clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2005-01-01')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(null, Date::create('2006-01-01'))
+			->clip(DateRange::create(null, Date::create('2006-01-01')));
+		$this->assertNull($clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(null, Date::create('2006-01-01'))
+			->clip(DateRange::create(null, Date::create('2007-01-01')));
+		$this->assertNull($clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(null, Date::create('2006-01-01'))
+			->clip(DateRange::create(Date::create('2005-01-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2005-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(null, Date::create('2006-01-01'))
+			->clip(DateRange::create(Date::create('2006-01-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getEnd()->toDate());
+		try {
+			DateRange::create(null, Date::create('2006-01-01'))
+				->clip(DateRange::create(Date::create('2007-01-01')));
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+		$clip = DateRange::create(null, Date::create('2006-01-01'))
+			->clip(DateRange::create(Date::create('2005-01-01'), Date::create('2005-02-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2005-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2005-02-01')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(null, Date::create('2006-01-01'))
+			->clip(DateRange::create(Date::create('2005-06-01'), Date::create('2006-01-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2005-06-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(null, Date::create('2006-01-01'))
+			->clip(DateRange::create(Date::create('2005-06-01'), Date::create('2006-06-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2005-06-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(null, Date::create('2006-01-01'))
+			->clip(DateRange::create(Date::create('2006-01-01'), Date::create('2006-06-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getEnd()->toDate());
+		try {
+			DateRange::create(null, Date::create('2006-01-01'))
+				->clip(DateRange::create(Date::create('2006-05-01'), Date::create('2006-06-01')));
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+
+		$clip = DateRange::create(Date::create('2006-01-01'))
+			->clip(DateRange::create());
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertNull($clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		try {
+			DateRange::create(Date::create('2006-01-01'))
+				->clip(DateRange::create(null, Date::create('2005-06-01')));
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+		$clip = DateRange::create(Date::create('2006-01-01'))
+			->clip(DateRange::create(null, Date::create('2006-01-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'))
+			->clip(DateRange::create(null, Date::create('2007-01-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2007-01-01')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'))
+			->clip(DateRange::create(Date::create('2005-01-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertNull($clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'))
+			->clip(DateRange::create(Date::create('2006-01-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertNull($clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'))
+			->clip(DateRange::create(Date::create('2007-01-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertNull($clip->getEnd());
+		$this->assertEquals(Date::create('2007-01-01')->toDate(), $clip->getStart()->toDate());
+		try {
+			DateRange::create(Date::create('2006-01-01'))
+				->clip(DateRange::create(Date::create('2005-01-01'), Date::create('2005-06-01')));
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+		$clip = DateRange::create(Date::create('2006-01-01'))
+			->clip(DateRange::create(Date::create('2005-01-01'), Date::create('2006-01-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'))
+			->clip(DateRange::create(Date::create('2005-06-01'), Date::create('2006-06-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-06-01')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'))
+			->clip(DateRange::create(Date::create('2006-01-01'), Date::create('2006-06-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-06-01')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'))
+			->clip(DateRange::create(Date::create('2007-01-01'), Date::create('2007-06-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2007-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2007-06-01')->toDate(), $clip->getEnd()->toDate());
+
+		$clip = DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+			->clip(DateRange::create());
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-12-31')->toDate(), $clip->getEnd()->toDate());
+		try {
+			DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+				->clip(DateRange::create(null, Date::create('2005-06-01')));
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+		$clip = DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+			->clip(DateRange::create(null, Date::create('2006-01-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+			->clip(DateRange::create(null, Date::create('2006-06-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-06-01')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+			->clip(DateRange::create(null, Date::create('2006-12-31')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-12-31')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+			->clip(DateRange::create(null, Date::create('2007-12-31')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-12-31')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+			->clip(DateRange::create(Date::create('2005-01-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-12-31')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+			->clip(DateRange::create(Date::create('2006-06-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-06-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-12-31')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+			->clip(DateRange::create(Date::create('2006-12-31')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-12-31')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-12-31')->toDate(), $clip->getEnd()->toDate());
+		try {
+			DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+				->clip(DateRange::create(Date::create('2007-06-01')));
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+		$clip = DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+			->clip(DateRange::create(Date::create('2005-01-01'), Date::create('2007-12-31')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-12-31')->toDate(), $clip->getEnd()->toDate());
+		try {
+			DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+				->clip(DateRange::create(Date::create('2005-01-01'), Date::create('2005-06-01')));
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+		$clip = DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+			->clip(DateRange::create(Date::create('2005-01-01'), Date::create('2006-01-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+			->clip(DateRange::create(Date::create('2005-01-01'), Date::create('2006-06-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-06-01')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+			->clip(DateRange::create(Date::create('2005-01-01'), Date::create('2006-12-31')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-12-31')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+			->clip(DateRange::create(Date::create('2006-01-01'), Date::create('2006-06-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-06-01')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+			->clip(DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-12-31')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+			->clip(DateRange::create(Date::create('2006-01-01'), Date::create('2007-12-31')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-12-31')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+			->clip(DateRange::create(Date::create('2006-06-01'), Date::create('2006-07-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-06-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-07-01')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+			->clip(DateRange::create(Date::create('2006-06-01'), Date::create('2006-12-31')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-06-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-12-31')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+			->clip(DateRange::create(Date::create('2006-06-01'), Date::create('2007-12-31')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-06-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-12-31')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+			->clip(DateRange::create(Date::create('2006-12-31'), Date::create('2007-12-31')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-12-31')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-12-31')->toDate(), $clip->getEnd()->toDate());
+		try {
+			DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+				->clip(DateRange::create(Date::create('2007-06-01'), Date::create('2007-12-31')));
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+	}
+
+	public function testLightCopyOnClip()
+	{
+		$clip = DateRange::create()->lightCopyOnClip(DateRange::create());
+		$this->assertInstanceOf(DateRange::class, $clip);
+		$this->assertNull($clip->getStart());
+		$this->assertNull($clip->getEnd());
+
+		$clip = DateRange::create(null, Date::create('2006-01-01'))
+			->lightCopyOnClip(DateRange::create());
+		$this->assertNull($clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(null, Date::create('2006-01-01'))
+			->lightCopyOnClip(DateRange::create(null, Date::create('2005-01-01')));
+		$this->assertNull($clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2005-01-01')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(null, Date::create('2006-01-01'))
+			->lightCopyOnClip(DateRange::create(null, Date::create('2006-01-01')));
+		$this->assertNull($clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(null, Date::create('2006-01-01'))
+			->lightCopyOnClip(DateRange::create(null, Date::create('2007-01-01')));
+		$this->assertNull($clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(null, Date::create('2006-01-01'))
+			->lightCopyOnClip(DateRange::create(Date::create('2005-01-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2005-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(null, Date::create('2006-01-01'))
+			->lightCopyOnClip(DateRange::create(Date::create('2006-01-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getEnd()->toDate());
+		try {
+			$clip = DateRange::create(null, Date::create('2006-01-01'))
+				->lightCopyOnClip(DateRange::create(Date::create('2007-01-01')));
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+		$clip = DateRange::create(null, Date::create('2006-01-01'))
+			->lightCopyOnClip(DateRange::create(Date::create('2005-01-01'), Date::create('2005-02-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2005-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2005-02-01')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(null, Date::create('2006-01-01'))
+			->lightCopyOnClip(DateRange::create(Date::create('2005-06-01'), Date::create('2006-01-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2005-06-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(null, Date::create('2006-01-01'))
+			->lightCopyOnClip(DateRange::create(Date::create('2005-06-01'), Date::create('2006-06-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2005-06-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(null, Date::create('2006-01-01'))
+			->lightCopyOnClip(DateRange::create(Date::create('2006-01-01'), Date::create('2006-06-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getEnd()->toDate());
+		try {
+			DateRange::create(null, Date::create('2006-01-01'))
+				->lightCopyOnClip(DateRange::create(Date::create('2006-05-01'), Date::create('2006-06-01')));
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+
+		$clip = DateRange::create(Date::create('2006-01-01'))
+			->lightCopyOnClip(DateRange::create());
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertNull($clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		try {
+			DateRange::create(Date::create('2006-01-01'))
+				->lightCopyOnClip(DateRange::create(null, Date::create('2005-06-01')));
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+		$clip = DateRange::create(Date::create('2006-01-01'))
+			->lightCopyOnClip(DateRange::create(null, Date::create('2006-01-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'))
+			->lightCopyOnClip(DateRange::create(null, Date::create('2007-01-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2007-01-01')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'))
+			->lightCopyOnClip(DateRange::create(Date::create('2005-01-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertNull($clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'))
+			->lightCopyOnClip(DateRange::create(Date::create('2006-01-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertNull($clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'))
+			->lightCopyOnClip(DateRange::create(Date::create('2007-01-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertNull($clip->getEnd());
+		$this->assertEquals(Date::create('2007-01-01')->toDate(), $clip->getStart()->toDate());
+		try {
+			DateRange::create(Date::create('2006-01-01'))
+				->lightCopyOnClip(DateRange::create(Date::create('2005-01-01'), Date::create('2005-06-01')));
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+		$clip = DateRange::create(Date::create('2006-01-01'))
+			->lightCopyOnClip(DateRange::create(Date::create('2005-01-01'), Date::create('2006-01-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'))
+			->lightCopyOnClip(DateRange::create(Date::create('2005-06-01'), Date::create('2006-06-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-06-01')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'))
+			->lightCopyOnClip(DateRange::create(Date::create('2006-01-01'), Date::create('2006-06-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-06-01')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'))
+			->lightCopyOnClip(DateRange::create(Date::create('2007-01-01'), Date::create('2007-06-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2007-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2007-06-01')->toDate(), $clip->getEnd()->toDate());
+
+		$clip = DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+			->lightCopyOnClip(DateRange::create());
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-12-31')->toDate(), $clip->getEnd()->toDate());
+		try {
+			DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+				->lightCopyOnClip(DateRange::create(null, Date::create('2005-06-01')));
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+		$clip = DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+			->lightCopyOnClip(DateRange::create(null, Date::create('2006-01-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+			->lightCopyOnClip(DateRange::create(null, Date::create('2006-06-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-06-01')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+			->lightCopyOnClip(DateRange::create(null, Date::create('2006-12-31')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-12-31')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+			->lightCopyOnClip(DateRange::create(null, Date::create('2007-12-31')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-12-31')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+			->lightCopyOnClip(DateRange::create(Date::create('2005-01-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-12-31')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+			->lightCopyOnClip(DateRange::create(Date::create('2006-06-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-06-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-12-31')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+			->lightCopyOnClip(DateRange::create(Date::create('2006-12-31')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-12-31')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-12-31')->toDate(), $clip->getEnd()->toDate());
+		try {
+			DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+				->lightCopyOnClip(DateRange::create(Date::create('2007-06-01')));
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+		$clip = DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+			->lightCopyOnClip(DateRange::create(Date::create('2005-01-01'), Date::create('2007-12-31')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-12-31')->toDate(), $clip->getEnd()->toDate());
+		try {
+			DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+				->lightCopyOnClip(DateRange::create(Date::create('2005-01-01'), Date::create('2005-06-01')));
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+		$clip = DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+			->lightCopyOnClip(DateRange::create(Date::create('2005-01-01'), Date::create('2006-01-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+			->lightCopyOnClip(DateRange::create(Date::create('2005-01-01'), Date::create('2006-06-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-06-01')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+			->lightCopyOnClip(DateRange::create(Date::create('2005-01-01'), Date::create('2006-12-31')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-12-31')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+			->lightCopyOnClip(DateRange::create(Date::create('2006-01-01'), Date::create('2006-06-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-06-01')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+			->lightCopyOnClip(DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-12-31')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+			->lightCopyOnClip(DateRange::create(Date::create('2006-01-01'), Date::create('2007-12-31')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-01-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-12-31')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+			->lightCopyOnClip(DateRange::create(Date::create('2006-06-01'), Date::create('2006-07-01')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-06-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-07-01')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+			->lightCopyOnClip(DateRange::create(Date::create('2006-06-01'), Date::create('2006-12-31')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-06-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-12-31')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+			->lightCopyOnClip(DateRange::create(Date::create('2006-06-01'), Date::create('2007-12-31')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-06-01')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-12-31')->toDate(), $clip->getEnd()->toDate());
+		$clip = DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+			->lightCopyOnClip(DateRange::create(Date::create('2006-12-31'), Date::create('2007-12-31')));
+		$this->assertInstanceOf(Date::class, $clip->getStart());
+		$this->assertInstanceOf(Date::class, $clip->getEnd());
+		$this->assertEquals(Date::create('2006-12-31')->toDate(), $clip->getStart()->toDate());
+		$this->assertEquals(Date::create('2006-12-31')->toDate(), $clip->getEnd()->toDate());
+		try {
+			DateRange::create(Date::create('2006-01-01'), Date::create('2006-12-31'))
+				->lightCopyOnClip(DateRange::create(Date::create('2007-06-01'), Date::create('2007-12-31')));
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+	}
+
+	public function testGetStartStamp()
+	{
+		$date = Date::makeToday();
+		$dateNew = $date->spawn("+1 week");
+		$dateRange = DateRange::create();
+		$this->assertNull($dateRange->getStartStamp());
+
+		$dateRange->setStart($date);
+		$this->assertIsInt($dateRange->getStartStamp());
+		$this->assertEquals($date->getDayStartStamp(), $dateRange->getStartStamp());
+		$dateRange->setStart($dateNew);
+		$this->assertIsInt($dateRange->getStartStamp());
+		$this->assertEquals($dateNew->getDayStartStamp(), $dateRange->getStartStamp());
+		$dateRange->dropStart();
+		$this->assertNull($dateRange->getStartStamp());
+	}
+
+	public function testGetEndStamp()
+	{
+		$date = Date::makeToday();
+		$dateNew = $date->spawn("+1 week");
+		$dateRange = DateRange::create();
+		$this->assertNull($dateRange->getEndStamp());
+
+		$dateRange->setEnd($date);
+		$this->assertIsInt($dateRange->getEndStamp());
+		$this->assertEquals($date->getDayEndStamp(), $dateRange->getEndStamp());
+		$dateRange->setEnd($dateNew);
+		$this->assertIsInt($dateRange->getEndStamp());
+		$this->assertEquals($dateNew->getDayEndStamp(), $dateRange->getEndStamp());
+		$dateRange->dropEnd();
+		$this->assertNull($dateRange->getEndStamp());
+	}
+
+	public function testIsOneDay()
+	{
+		$this->assertFalse(DateRange::create()->isOneDay());
+		$this->assertFalse(DateRange::create(Date::makeToday())->isOneDay());
+		$this->assertFalse(DateRange::create(null, Date::makeToday())->isOneDay());
+		$this->assertFalse(DateRange::create(Date::makeToday(), Date::create("+1 week"))->isOneDay());
+		$this->assertTrue(DateRange::create(Date::create("+1 week"), Date::create("+1 week"))->isOneDay());
+	}
+
+	public function testToTimestampRange()
+	{
+		$tsRange = DateRange::create()->toTimestampRange();
+		$this->assertInstanceOf(TimestampRange::class, $tsRange);
+		$this->assertNull($tsRange->getStart());
+		$this->assertNull($tsRange->getEnd());
+
+		$start = Date::makeToday();
+		$end = $start->spawn("+1 week");
+		$tsRange = DateRange::create($start)->toTimestampRange();
+		$this->assertInstanceOf(Timestamp::class, $tsRange->getStart());
+		$this->assertNull($tsRange->getEnd());
+		$this->assertEquals($start->getDayStartStamp(), $tsRange->getStartStamp());
+
+		$tsRange = DateRange::create($start, $end)->toTimestampRange();
+		$this->assertInstanceOf(Timestamp::class, $tsRange->getStart());
+		$this->assertInstanceOf(Timestamp::class, $tsRange->getEnd());
+		$this->assertEquals($start->getDayStartStamp(), $tsRange->getStartStamp());
+		/** use day start stamp because Date to Timestamp - result time 00:00:00 */
+		$this->assertEquals($end->getDayStartStamp(), $tsRange->getEndStamp());
+
+		$tsRange = DateRange::create(null, $end)->toTimestampRange();
+		$this->assertNull($tsRange->getStart());
+		$this->assertInstanceOf(Timestamp::class, $tsRange->getEnd());
+		/** use day start stamp because Date to Timestamp - result time 00:00:00 */
+		$this->assertEquals($end->getDayStartStamp(), $tsRange->getEndStamp());
+	}
+
+	public function testCheckType()
+	{
+		$dateRange = new \OnPHP\Tests\TestEnvironment\Main\Base\DateRange();
+		$dateRange->checkType(Date::class);
+		$dateRange->checkType(Date::makeToday());
+		try {
+			$dateRange->checkType(DateRange::class);
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+	}
+
+	public function testGetObjectName()
+	{
+		$dateRange = new \OnPHP\Tests\TestEnvironment\Main\Base\DateRange();
+		$this->assertEquals($dateRange->getObjectName(), Date::class);
 	}
-}
-?>
\ No newline at end of file
+}
\ No newline at end of file
diff --git a/tests/TestEnvironment/Main/Base/DateRange.php b/tests/TestEnvironment/Main/Base/DateRange.php
new file mode 100644
index 0000000000..5a029351ff
--- /dev/null
+++ b/tests/TestEnvironment/Main/Base/DateRange.php
@@ -0,0 +1,25 @@
+<?php
+
+namespace OnPHP\Tests\TestEnvironment\Main\Base;
+
+use OnPHP\Core\Exception\WrongArgumentException;
+
+class DateRange extends \OnPHP\Main\Base\DateRange
+{
+	/**
+	 * @param $value
+	 * @throws WrongArgumentException
+	 */
+	public function checkType($value): void
+	{
+		parent::checkType($value);
+	}
+
+	/**
+	 * @return string
+	 */
+	public function getObjectName(): string
+	{
+		return parent::getObjectName();
+	}
+}
\ No newline at end of file